#### Answer

$r=\dfrac{M-C}{C}$

#### Work Step by Step

Using the properties of equality, in terms of $
r
,$ the given formula, $
M=C(1+r)
,$ is equivalent to
\begin{array}{l}\require{cancel}
M=C+Cr
\\\\
M-C=Cr
\\\\
\dfrac{M-C}{C}=r
\\\\
r=\dfrac{M-C}{C}
.\end{array}