The function has no maximum since it is strictly increasing with any positive change of x or y.
Finding the partial derivatives with respect to x and y give:
f_x(x,y) = 18x
f_y(x,y)= 20y
Setting both equal to 0, gives us the coordinates of the only critical point (0,0).
f(0,0) = 0. The minimum is therefore, 0.
