Elimination in math. Please help

The sum of two numbers is 41 and their difference is 5. What are the numbers?

Let then 2 numbers be a and b.
a+b=41 --- (1)
a-b=5 --- (2)
Both (1) & (2) have +a, let's get rid of it by taking (1) minus (2).
a+b=41
-) a-b=5
2b=36
b= 18
then you can substitute b=18 into any equation (either (1) or (2)) to get a. a=23.

a+b=41
a-b=5

2a=46
a=23
b=18