Please Help Soon!thanks
A river follows the path y = f(z) where x, y are in kilometers. Near the
sea, it widens into a lagoon, then narrows again at its mouth. At the point
(x, y), the depth of the lagoon is given by D(x, y) = 40−160(y−f(x))2 − 40x2 meters. The lagoon itself is described by...