AHSME 1950 Problem 32

A $25$ foot ladder is placed against a vertical wall of a building. The foot of the ladder is $7$ feet from the base of the building. If the top of the ladder slips $4$ feet, then the foot of the ladder will slide: $\textbf{(A)}\ 9\text{ ft} \textbf{(B)}\ 15\text{ ft} \textbf{(C)}\ 5\text{ ft} \textbf{(D)}\ 8\text{ ft} \textbf{(E)}\ 4\text{ ft}$