Answer
$M=\dfrac{P-C}{C}$
Work Step by Step
Subtract by $C$ to both sides:
$P-C=C+MC-C
\\P-C=MC$
Divide by $C$ on both sides:
$\dfrac{P-C}{C}=\dfrac{MC}{C}
\\\dfrac{P-C}{C}=M
\\M=\dfrac{P-C}{C}$
You can help us out by revising, improving and updating this answer.
Update this answerAfter you claim an answer you’ll have 24 hours to send in a draft. An editor will review the submission and either publish your submission or provide feedback.