1971 AHSME Problem 15

An aquarium on a level table has rectangular faces and is 10 inches wide and 8 inches high. When it was tilted, the water in it covered an 8\times 10 end but only \tfrac{3}{4} of the rectangular room. The depth of the water when the bottom was again made level, was

\textbf{(A) }2\textstyle{\frac{1}{2}}"\qquad \textbf{(B) }3"\qquad \textbf{(C) }3\textstyle{\frac{1}{4}}"\qquad \textbf{(D) }3\textstyle{\frac{1}{2}}"\qquad \textbf{(E) }4"

Full credit goes to MAA for authoring these problems. These problems were taken on the AOPS website.