The sum of two numbers is 52. the difference of the same two numbers is 20. find the two numbers

To solve this problem we have to make system of equations.

From the first equation lets find value of a in times of b
a=52-b
Now we can substitute it into second equation
52-b-b=20  
52-2b=20      /-52 both sides
-2b=20-52
-2b=-32    :(-2) divide both sides by -2
b=16
Now we can back substitute to the first equation
a=52-b
a=52-16
a=36

So the result is