If the volume of the rectangular prism is
120 cu units, then its height is units.

The correct option is A 30
Volume of the rectangular prism
= $\text{Area of the base}\times \text{height}$
= $4\times h$ cu units,
where $h$ is the height.

But, volume is given to be 120 cu units.

$⟹120=4h$
$⟹\frac{120}{4}=h=30\text{units}$

Thus, the height of the rectangular prism is 30 units.