How do you solve equations? for example, y+12=8

To solve y + 12 = 8 you need to separate the variable on one side. In this case it's the y. Now, how can we separate the y? We see the 12 on the left side. It's also the same side as y. Let's take it out. To do this we subtract 12. But we also do it on the right side too in order to keep the balance. 

y + (12 - 12) = 8 - 12

y = -4

Now we now y is equal to -4