$\text{Volume of a prism}=(\text{area of base})(\text{height})$

Consider the prism's volume in terms of multiple layers that are each one unit high and stacked depending on the height.

Solve for the volume of the prism if it had only a $1$-unit-high layer and then for the actual respective number of layers based on the height.

Volume ($1$ unit layer): $(50\text{ m}·10\ \text{m})(1\ \text{m})(500\ \text{m})(1\ \text{m})=500\ \text{m}^3$
Volume (Total): $(50\ \text{m}·10\ \text{m})(10\ \text{m})(500\ \text{m})(10\ \text{m})=5000\ \text{m}^3$

See part (a).