The sum of two numbers is 70. one number is 8 more than the other. what's the smaller number?

X=8+y
x+y=70

Rewrite the first equation to x-y=8
Copy the second equation   x+y=70

Add the two equations and you get 2x=78
Therefore, x=39. Since this is the bigger number the smaller number(y) would have to be 31 because you subtract 8 from x which is 39. 39 is your answer. 

Atranslation 6 units to the right and 4 down