15m-12-12m=16 what's the answer

It's more helpful to learn how to solve equations than to just give you the answer.

Here's a similar equation...
7x - 4 - 9x = 14

We need to get all the x-terms on one side and all the non-x-terms on the other side.

The most important thing to remember is... "What you do to one side you must do to the other side."
7x - 4 - 9x = 14
+ 4 +4 (Add four to both sides.)
7x - 9x = 18 (Just ignore the x, and subtract 7 from 9.)
-2x = 18
(Divide by -2 to isolate the x.)
x = 18/-2
x = -9

thankyou

Glad to help. :)