find two numbers such that one of them exceeds the other by 13 and their sum is 77
let two numbers be X, y
X - y = 13
X + y = 77
by adding
2x = 100
X =50
so 50 - y = 13
so y = 37
X - y = 13
X + y = 77
by adding
2x = 100
X =50
so 50 - y = 13
so y = 37