a$)$ Determine the following integral:

$I=o{\displaystyle \underset{\phantom{}}{\overset{\phantom{}}{}}}(2x^2-y^2)dx+(x^2+y^2)dy$

along the closed line shown in the figure below in the counterclockwise direction, where the upper semicircle is described by the equation $x^2+y^2=4$ and the lower semicircle by $x^2+y^2=1$

b$)$ As an alternative determine the same integral I by using Green's Theorem.