Answer
$(2a+b)^{3} $
Work Step by Step
$(a+b)^{n}=\left(\begin{array}{l}
n\\
0
\end{array}\right)a^{n}+\left(\begin{array}{l}
n\\
1
\end{array}\right)a^{n-1}b+\left(\begin{array}{l}
n\\
2
\end{array}\right)a^{n-2}b^{2}+\cdots+\left(\begin{array}{l}
n\\
n
\end{array}\right)b^{n}$
-------------------
$8a^{3}=(2a)^{3}$ and $b^{3}=(b)^{3}$
lead us to check whether the expression equals $(2a+b)^{3} $
$(2a+b)^{3} =\left(\begin{array}{l}
3\\
0
\end{array}\right)(2a)^{3}b^{0}+\left(\begin{array}{l}
3\\
1
\end{array}\right)(2a)^{2}b^{1}+\left(\begin{array}{l}
3\\
2
\end{array}\right)(2a)^{1}b^{2}+\left(\begin{array}{l}
3\\
3
\end{array}\right)(2a)^{0}b^{3}$
$=8a^{3}+12a^{2}b+6ab^{2}+b^{3}$
It does.
