3) Use Green's theorem to evaluate the line integral along the given positively oriented, simple closed curve
(a) $\int_C ye^x dx + 2e^x dy$ where $C$ is the rectangle with vertices, $(0, 0), (3, 0), (3, 4), (0, 4)$,
(b) $\int_C (x^2 + y^2) dx + (x^2 - y^2) dy$ where $C$ is the triangle with vertices $(0, 0), (2, 1)$, and $(0, 1)$.
(c) $\int_C y^3 dx - x^3 dy$ where $C$ is the circle $x^2 + y^2 = 4$,
(d) $\int_C (y + e^{\sqrt{x}}) dx + (2x + cos(y^2)) dy$ where $C$ is the boundary of the region enclosed by the parabolas $y = x^2$ and $x = y^2$.
