Answer
$30=2\cdot 3\cdot 5$
$56=2\cdot 2\cdot 2\cdot 7$
$72=2\cdot 2\cdot 2\cdot 3\cdot 3$
Work Step by Step
$a.$
$ \begin{array}{cccccccc}
& & & & 30 & & & \\
& & & & \swarrow\searrow & & & & \\
& & & 2 & \times & 15 & & \\
& & & & & \swarrow\searrow & & & \\
& & & & 3 & \times & 5 &
\end{array}$
$30=2\cdot 3\cdot 5$
$b.$
$ \begin{array}{cccccccc}
& & 56 & & & \\
& & \swarrow\searrow & & & & \\
& 2 & \times & 28 & & \\
& & & \swarrow\searrow & & & \\
& & 2 & \times & 14 & \\
& & & & \swarrow\searrow & & \\
& & & 2 & \times & 7
\end{array}$
$56=2\cdot 2\cdot 2\cdot 7$
$c. \\
\begin{array}{llllllll}
& & 72 & & & & \\
& & \swarrow\searrow & & & & & \\
& 2 & \times & 36 & & & \\
& & & \swarrow\searrow & & & & \\
& & 2 & \times & 18 & & \\
& & & & \swarrow\searrow & & & \\
& & & 2 & \times & 9 & \\
& & & & & \swarrow\searrow & & \\
& & & & 3 & \times & 3
\end{array}$
$72=2\cdot 2\cdot 2\cdot 3\cdot 3$