Consider a function f(x, y) = 2x2 - by + a for some fixed constant a. Then we may define a surface by z = f(x, y) Some particular level curves for that surface are shown below, with the corresponding z values or levels shown in the legend underneath the plot. Deduce the values of a and b 6 y -4 2 -1. . . . . 0 . . .. -2 -6 2=-4 ." 2=8 -- z=20