In the diagram, $\triangle A B C$ is isosceles and its area is 240 . The $y$-coordinate of $A$ is
(A) 6
(B) 12
(C) 18
(D) 24
(E) 48
The base of $\triangle A B C$ (that is, $B C$ ) has length 20 .

Since the area of $\triangle A B C$ is 240 , then $240=\frac{1}{2} b h=\frac{1}{2}(20) h=10 h$, so $h=24$.

Since the height of $\triangle A B C$ (from base $B C$ ) is 24 , then the $y$-coordinate of $A$ is 24 .

ANSWER: (D)