Downloading Rating from firebase, first rating always shows up as nan - swift

Question

So I'm trying to download the ratings from firebase database and then show them on a Mapbox subtitle. however the first and only the first infographic shows up as nan.
Ive tried dispatches and times, and unfortunately nothing seems to be working. I have no clue what to do.
func showCarIcon() {
ref = Database.database().reference()
ref.child("location").observe(.childAdded) { (snapshot:DataSnapshot) in
if let dict = snapshot.value as? [String:AnyObject] {
if dict["Activity"] as! String == "Car" {
let longitude = dict["Longitude"] as! String
let lattitude = dict["Lattitude"] as! String
let title = dict["Title"] as! String
let key = dict["id"] as! String
self.carIconArray.insert(coordinate(title: title, carLat: lattitude, carLng: longitude, idKey: key), at: 0)
let n = self.carIconArray.count
for carMarker in 1...n {
let location = CLLocationCoordinate2D(latitude: Double(lattitude)!, longitude: Double(longitude)!)
let carMarker = CustomPointAnnotation(coordinate: location)
var totalrating = Double(0)
var ratingcount = Double(0)
self.ref.child("location/\(key)/Ratings").observe(.value, with: { (snapshot: DataSnapshot) in
for childSnap in snapshot.children.allObjects {
let snap = childSnap as! DataSnapshot
let rating = snap.value as! Double
totalrating += rating
ratingcount += 1
}
let netRating = Double(totalrating/ratingcount)
let final = Double(round(100*netRating)/100)
carMarker.reuseIdentifier = "carMarker"
carMarker.image = UIImage(named: "carPin")
carMarker.title = title
carMarker.subtitle = "\(final)/5.0"
carMarker.key = key
// add Car marke to array
self.arrCarMarkers.append(carMarker)
// add array to map
self.mapView.addAnnotations(self.arrCarMarkers)
})
}
}
}
}
}
JSON Tree
"location" : {
"-LkKU4hLZQfI2XDdljQk-LkKU9ZkGYnP82pKeZoe-LkKUD50ouEXYT9LuzSw" : {
"Activity" : "Car",
"Coordinate" : "-35.13815006034659,138.53838695658027",
"Description" : "H",
"Difficulty" : "Medium",
"Lattitude" : "-35.13815006034659",
"Longitude" : "138.53838695658027",
"Ratings" : {
"WgPMwulBX9ScTHqa0htPyr355TQ2" : 4
"Bfodb4309gn30fnofjlnd3u93438" : 5
},
"Title" : "H",
"id" : "-LkKUD50ouEXYT9LuzSw",
}
}
Please can someone help me!!