find the volume of the solid that lies under the hyperbolic paraboloid z = 3y2 − x2 5 and above the rectangle r = [−1, 1] × [1, 2].
Find the average value of f over the given rectangle
f(x,y) = 2 x2 y, R has vertices (-4,0), (-4,5), (4,5), (4,0)