Answer
$n=4$
Work Step by Step
$$\begin{align*}
36&=9n &\text{Combine like terms.}\\
\\\frac{36}{9}&=\frac{9n}{9} &\text{Divide both sides by 9.}\\
\\4&=n&\text{Simplify.}
\end{align*}$$
Check the answer by substituting $4$ to the variable in the given equation.
$$\begin{align*}
36&=13n-4n\\
36&\stackrel{?}{=}13(4)-4(4)\\
36&\stackrel{?}{=}52-16\\
36&\stackrel{\checkmark}{=}36
\end{align*}$$
Thus, the solution is $n=4$.
