Answer
$$\frac{1}{36} (3x+8) ^{12}+c$$
Work Step by Step
Given $$\int (3x+8)^{11}d x$$
Let
$$u=3x+8 \ \ \ \Rightarrow \ \ du=3dx $$
then
\begin{align*}
\int (3x+8)^{11}d x&=\frac{1}{3} \int u^{11}du \\
&=\frac{1}{36} u^{12}+c\\
&=\frac{1}{36} (3x+8) ^{12}+c
\end{align*}
