On the first play of the game a running back gained 7 yards. on the next play he lost 19 yards find the change in yards i'm the 2 plays

The question isn't the best worded so i'm making a lot of assumptions here:

First play: gained 7 yards
Second play: lost 19 yards
Find the change in yards.

The question is asking what is the change to make +7 into -19. 
You can do this however you like, i.e. in your head

If you cannot do it in your head I suggest you use the rule:
[Larger Number] - [Smaller Number]
to find the difference/change 
+7 - -19    (to negatives make a positive rule)
= +7 + 19
= +26  
The answer is +26 change in yards