It's pretty simple! So it looks like you are learning proportions. You would cross multiply to achieve your answer.
First, let's do your first problem:
2 12 --- = ---- 5 n
You would take 5 and multiply it by 12 and get 60! Then you would do the same with 2 times n, giving you 2n (because you do not know what n represents YET.)
Now you should have this: 60=2n OR 2n=60
We must isolate our variable, in order to do that, get rid of two! But how? You would do this by dividing 2n by 2. Yet in equations, when you do something to one side, you must do it to the other because they must be EQUAL! (hence the "equa-" in equation)
