The right rectangular prism below is made of equal-sized cubes the side length of each cube is 2 1/2 inches . what’s is the volume in cubic images of the right rectangular prism?

We know that

volume of one cube=b³
where 
b is the length side of cube
b=2 1/2 in> (2*2+1)/2> 5/2 in
volume of one cube=(5/2)³> 125/8 in³

volume of the prism=[volume of one cube]*5*2*4
volume of the prism=[volume of one cube]*40
volume of the prism=[125/8]*40> 625 in³

the answer is
the volume of the prism is equal to the volume of 40 cubes
the volume of the prism is equal to 625 in³

Idon't know what's the answer lol