well there are a few ways to solve this I will do it the easiest way for me:
-4y + 13 = y-7 we need to get the y on one side and the number on one side such that we have y= #
so lets subtract 13 from both sides
-4y + 13 - 13 = y - 7 - 13
-4y + 0 = y - 20
-4y= y - 20 (no need to write the 0) now subtract y from both sides
-4y - 1y= y - y - 20
-5y = 0y - 20
-5y = -20 now divide both sides by -5
y = 4 Is our one and only answer
Check: plug in y = 4
-4(4) + 13 = 4 - 7
-16+13=4-7
-3=-3 it checks out