Find two numbers whose sum is 29 and whose difference is 15

The two numbers are 22 and 7.
22 + 7 = 29
22 - 7 = 15
here is how we can find these numbers;
let a and b are two numbers
a + b = 29
a - b = 15
a   = 15 + b
now put this value of a in any of the equation
a + b = 29
15 + b  + b = 29
15 + 2b = 29
2b = 29 - 15
2b = 14
b = 7
now put the value of b to find the value of a;
a = 15 + b = 15 + 7 = 22
a = 22