Aright rectangular prism and an oblique triangular prism are both 12 centimeters tall and have the same volume. what statement must be true about the two solids?

Check the picture.

The bases of the 2 prisms are on 2 parallel planes, a and b.

Let c be a third plane, between a and b, parallel to both.

Then, 

 the cross-sections A and B , of the 2 prisms, formed by plane c, have Equal Areas,

this is by Cavalier's Principle.