1982 AHSME Problem 9

A vertical line divides the triangle with vertices (0,0), (1,1), and (9,1) in the xy\text{-plane} into two regions of equal area. The equation of the line is x=

\text {(A)} 2.5 \qquad \text {(B)} 3.0 \qquad \text {(C)} 3.5 \qquad \text {(D)} 4.0\qquad \text {(E)} 4.5

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