Given:
2 numbers whose sum is 23 and the difference is 11
Let the numbers are (x) and (y)
so, we have the following equations:

Solve the equations to find (x) and(y)
Add the equations will cancel the value of (y) then solve for x

From the first equation: y = 23 - x
substitute with x to find y

So, the answer will be the numbers are 6, 17