The correct answer is 5 cm. We can find this by substituting the values we've been given into the formula for the volume of a rectangular prism.
V = lwh Volume of a rectangular prism
100 = 20h Substitute. Keep in mind that the base is length times width, so 20 accounts for both variables.
5 = h Divide both sides by 20
The height of the rectangular prism is 5 cm.
Hope this helps!