I cant find any solutions anywhere.. I know this is actually simple but i dont know how.. Here is my code..

var num1 : Int = 0 
var num2 : Int = 0 
var sum  : Int = 0 
var db = Firebase.firestore 
db.collection("collection1").document("doc1") 
.get()
.addOnSuccessListener { document ->
    num1 = document.data["num1"].toString().toInt() }

db.collection("collection2").document("doc1")
.get() .addOnSuccessListener { document ->
    num2 = document.data["num1"].toString().toInt() }

sum = num1 + num2 tvloading.text = sum.toString()

i know that the variables will work inside the query but i need to use variable outside the query so that i can add two variables from different collections.. please help