South African Mathematics Olympiad First Round

If $a$ and $b$ are positive integers such that $\frac{a}{b}=\frac{2}{3}$ and $a+b=80$, then the product $ab$ is equal to

(A) 1 500 (B) 1 599 (C) 1 667 (D) 1 596 (E) 1 536