How can I remember to set up an equation like this problem?

y – 15 = -7. (I know you have to drop down the +15 to both sides but then after that I get mixed up.) I need tips on how you do it. (Preferablly, lameance terms.)

I know the answer is 8 – 15 = 7 and 8 = y but, I fustrate myself and give up.