Volume, SM-Bank 010

A rectangular block of land has width 50 metres and length 85 metres.

In order to build a house, the builders dig a hole in the block of land.

The hole has the shape of a right-triangular prism,  .

The width = 20 m, length = 25 m and height = 4 m are shown in the diagram below.
 

Calculate the volume of the right-triangular prism, , giving your answer in cubic metres.  (2 marks)