13 Use the transformation u=3x+4y, v=x+4y to evaluate the given integral for the region R bounded by 3 3 the lines y = -x+3, y=-x+4, y=-x, and y = -x+1. R (3x²+16xy+16y²) dx dy SS (3x²+16xy + 16y²) dx dy = R (Simplify your answer.)