A right rectangular prism has a length of 2 1/2 feet, a width of 3 feet, and a height of 1 1/2 feet. Unit cubes with side lengths of 1/2 foot are added to completely fill the prism with no space remaining. What is the volume, in cubic feet, of the right rectangular prism

The statement "unit cubes with side lengths of 1/2 foot are added to fill the prism with no space remaining" is useless information so you can disregard that. All you need to know to calculate the volume is the length, width, and height.

Volume = length x width x height

Volume = (5/2) x 3 x 11/2

Volume = 15/2 x 11/2

Volume = 165/4

Volume = 41.25 ft cubed