A calculus problem by Rahil Sehgal

$\displaystyle\int \int_{D} 6x^2-40y \; dA$ , where $D$ is a triangle with vertices $(0,3), (1,1) , (5,3)$ . If the above multiple integral can be expressed in form of $- \dfrac{a}{b}$ , then enter the answer as $a+b$ .