In the given question, there are several information's that can be used to deduce the correct answer. It is already given that the average of 2 numbers is 25 and their difference is 8. So we can easily get two equations and from them we can find the two unknown numbers.
Let us assume one number to be = x
let us assume the second number to be = y
Then the first equation is
(x + y)/2 = 25
x + y = 50
The second equation is
x - y = 8
x = 8 + y
Now we replace the value of x from the second equation to the first
x + y = 50
8 + y + y = 50
2y + 8 = 50
2y = 50 - 8
2y = 42
y = 21
Now we put the value of y in any of the above equations to find the value of x
x + y = 50
x + 21 = 50
x = 50 - 21
= 29
So the two numbers are 29 and 21.
