Question 273532
You have two separate variables and two separate equations here. 

the first one, the sum of two numbers is 35 is set up like x+y=35
the second one, the difference between the numbers is 13 is set up like x-y=13

What you need to do is add the second equation to the first equation and solve for x.
To write it on paper woul look like the x written over the x, y over y etc. 

 x+y=35
 x-y=13
+______

2x =48          divide both sides by 2

 x=24

To find y plug the answer for x back into either of the original equations and you will end up with 11.

Check

24+11=35
24-11=13