can be factored using the "difference of squares" formula which is .
6*6=36 and 4*4=16; P*P=P^2 and M*M=M^2 -- from this we know that the two variables on each side of the minus sign are perfect squares. Now, see as to make it fit nicer to the formula.
So, .
If you forget the formula, you can always go backward on multiple-choice questions like this one. Use FOIL to expand your factored answers.