3. The function $g(u, v) = \left(\frac{u+v}{2}, \frac{u-v}{2}\right)$ maps the right-angled triangle W with vertices at $(-0,0)$, $(0,2)$, $(4,0)$ onto the triangle R with vertices at $(0,0)$, $(1, 1)$, $(-2,-2)$ shown below, (you do not have to prove this). You are are given the function $f(x,y) = x + 2y$. Use the composition $f \circ g(u,v)$ to evaluate $\iint_R f(x,y)dA$. (Any other method will earn you no points.) Write down your work.