The volume of her prism is 6×5×3=90 cubic inches. Add on the volume of the other prism: 90+120=210 cubic inches, so the total correctly adds up. Therefore Emily is probably correct. If Derek’s prism has a height of 6 inches and the height of Emily’s is 3 inches, the other two dimensions of Derek’s prism could be 4 and 5 inches. One of the dimensions of Emily’s prism matches 5 inches so that’s the side which lines up with Derek’s prism. The base width of Derek’s prism would be 4 inches, while the base width of Emily’s would be 6 inches. Both prisms would be 5 inches long.