3m +4

___ =12
4

Is this what you mean?

3m/4 + 4 = 12

If so, multiply both sides by 4.

3m + 16 = 48

Subtract 16 from both sides.

3m = 32

However, if you mean (3m+4)/4 = 12

Do the same first step.

3m +4 = 48

3m = 44

Either way, the last step is to divide both sides by 3.