#### Answer

$n=\dfrac{9(M-18)}{5}$

#### Work Step by Step

Using the properties of equality, in terms of $
n
$, the given equation, $
M=\dfrac{5}{9}n+18
$, is equivalent to
\begin{array}{l}
M-18=\dfrac{5}{9}n
\\\\
\left(\dfrac{9}{5} \right)(M-18)=\left( \dfrac{5}{9}n \right)\left(\dfrac{9}{5} \right)
\\\\
\\\\
n=\dfrac{9(M-18)}{5}
.\end{array}