How to summarise measured column but not from the beginning of the filtered values in powerBI - group-by

Question

I have two tables . I have created a table visual in power BI where I am combining the two values eg below :
Table 1 :
Site Name
Type
Area(m2)
A
Hospital
50
A
Education
100
B
Tech Lab
20
B
Office
70
B
Education
90
Table 2 :
Type
Usage (hr/m2)
Type
Hospital
100
Low
Education
500
Low
Tech Lab
50
Low
Office
200
Low
This visual also has a slicer:
Usage Type
Low
Medium
High
The slicer currently chosen is lets say "Low"
On my PowerBI visual ( a table) I am merging this two tables by "Type" to give me
Site Name
Type
Area
Usage(hr/m2)
A
Hospital
50
100
A
Education
100
500
B
Tech Lab
20
50
B
Office
70
200
B
Education
90
500
The end goal is to find the usage by site. In my head the equation should be :
For A :
TotalUsage[A]=Area[Hospital]*Usage[Hospital]+Area[Education]*Usage[Education] (50x100+100x500=55000)
TotalArea[A]=Area[Hospital]+Area[Education]=150
Usage[A]=TotalUsage[A]/TotalArea[A]=55000/150~366 hr/m2
How can I achieve this ?
I first created the visual as shown above(third table)
I did quick measures for total usage for each row. The displayed that on the third table.
However when I try to measure again , this type only grouped by Site, instead of following the above equation it sums the usage rows first (so 100+500=600), then sums the area ( 50+100=150) and then calculates the usage for site A giving 600/150 ( which is wrong! )

Answer 1

Use these measures:
Area Usage =
SUMX(
'Table 1',
'Table 1'[Area(m2)] * LOOKUPVALUE(
'Table 2'[Usage (hr/m2)],
'Table 2'[Type], SELECTEDVALUE('Table 1'[Type]),
'Table 2'[Usage Type], SELECTEDVALUE('Table 2'[Usage Type])
)
)
Total Usage =
SUMX(
VALUES('Table 1'[Type]),
[Area Usage]
)
Total Area = SUM('Table 1'[Area(m2)])
Usage = DIVIDE([Total Usage], [Total Area]))
and put everything together in a table