Form Calculator and display - forms

Question

is there anyway at all that i can get the number of lessons chosen to be multiplied by the lesson type and then displayed as a total near the form? It would be far easier for people filling out the form to have an automated calculation rather than having to have to calculate it themselves.
<h4>Lesson Form</h4>
<form action="mailer.php" data-validate="parsley" method="post" >
<p><strong>Full Name<span class="red">*</span></strong></p>
<input name="cf_name" data-required="true" class="send" type="text" />
<p><strong>Email Address<span class="red">*</span></strong></p>
<input name="cf_email" data-required="true" data-type="email" class="send" type="text" />
<p><strong>Cellphone No.<span class="red">*</span></strong></p>
<input name="cf_cell" data-required="true" class="send" type="text" />
<p><strong>Instrument Type<span class="red">*</span></strong></p>
<select name="cf_instrument" size="1" class="option" >
<option value="Piano">Piano</option>
<option value="Vocals">Vocals</option>
<option value="Guitar">Guitar</option>
<option value="Bass">Bass</option>
<option value="Flute">Flute</option></select>
<p><strong>Lesson Type<span class="red">*</span></strong></p>
<select name="cf_package_type" size="1" class="option">
<option value="Beginner Lesson - R100">Beginner Lesson - R100</option>
<option value="Advanced Lesson - R130">Advanced Lesson - R130</option>
<option value="Professional Lesson - R160">Professional Lesson - R160</option></select>
<p><strong>No. of Lessons<span class="red">*</span></strong></p>
<select id="number-of-lessons" name="cf_number" size="1" class="option" onchange='test()'>
<option value="1" selected="selected">1</option>
<option name="2" value="2">2</option>
<option name="3" value="3">3</option>
<option name="4" value="4">4</option></select>
<script src="js/datepair.js"></script>
<p><strong>Lesson Date & Time<span class="red">*</span></strong></p>
<p class="datepair" data-language="javascript">
<input type="text" name="cf_booking_date" class="date start" data-required="true" />
<input type="text" name="cf_start_time" class="time start" data-required="true" /> to
<input type="text" name="cf_end_time" class="time end" data-required="true" /></p>
<script src="js/datepair.js"></script>
<p id="lesson-2" class="datepair" data-language="javascript">
<input type="text" name="cf_booking_date" class="date start" data-required="true" />
<input type="text" name="cf_start_time" class="time start" data-required="true" /> to
<input type="text" name="cf_end_time" class="time end" data-required="true" /></p>
<script src="js/datepair.js"></script>
<p id="lesson-3" class="datepair" data-language="javascript">
<input type="text" name="cf_booking_date" class="date start" data-required="true" />
<input type="text" name="cf_start_time" class="time start" data-required="true" /> to
<input type="text" name="cf_end_time" class="time end" data-required="true" /></p>
<script src="js/datepair.js"></script>
<p id="lesson-4" class="datepair" data-language="javascript">
<input type="text" name="cf_booking_date" class="date start" data-required="true" />
<input type="text" name="cf_start_time" class="time start" data-required="true" /> to
<input type="text" name="cf_end_time" class="time end" data-required="true" /></p>
<!-- HIDDEN FIELD - HONEYPOT ANTI_SPAM -->
<input id="website" class="using" name="website" type="text" />
<!-- END -->
<input name="Submit" class="submit" value="Book Now" type="submit" /></form>
Would you so great if you could help me with this!

Answer 1

Here's a solution using Javascript.
explanation:
every time the option changes, I'm recalculating the multiplication of the chosen values.
HTML (simplified version of what you have. Notice how I changed the value of your options.)
<select id="lesson-type" onchange='calculate()'>
<option value="100">Beginner Lesson - R100</option>
<option value="130">Advanced Lesson - R130</option>
<option value="160">Professional Lesson - R160</option>
</select>
<select id="number-of-lessons" onchange='calculate()'>
<option value="1">1</option>
<option value="2">2</option>
<option value="3">3</option>
<option value="4">4</option>
</select>
<label id="result"></label>
JS:
function calculate() {
var l_type = document.getElementById("lesson-type").value;
var num_lessons = document.getElementById("number-of-lessons").value;
document.getElementById("result").innerHTML = l_type * num_lessons;
}
Edit:
in this Example I also call the function once the page loads.

Answer 2

If you want to create simple web calculator with Javascript I would recommend you to take a look at “Appizy”.
It converts instantly a spreadsheet into a standalone web calculation tool in HTML+CSS+JAVASCRIPT. You don’t need to hardcode the whole interface and calculation formulas!
Just create your working calculator with Open- or LibreOffice and then use Appizy.
I hope it can help. Best,
Nicolas