Calculate $\int_C \left(3 (x^2-y)\vec i + 6(y^2+x)\vec j\right) \cdot d\vec r$ if:

(a) $C$ is the circle $(x-2)^2+(y-7)^2=25$ oriented counterclockwise.
$\int_C \left(3 (x^2-y)\vec i + 6(y^2+x)\vec j\right) \cdot d\vec r =$

(b) $C$ is the circle $(x-a)^2+(y-b)^2=R^2$ in the $xy$-plane oriented counterclockwise.
$\int_C \left(3 (x^2-y)\vec i + 6(y^2+x)\vec j\right) \cdot d\vec r =$