The cost function c(w1, w2, y) of a firm gives the cost of producing y units of output when the wage of factor 1 is w1 and the wage of factor 2 is w2. Find the cost functions for the following firms:
a. A firm with production function f (x1, x2) =min{2x1, 3x2}
b. A firm with production function f (x1, x2) = 2x1 +3x2
c. A firm with production function f (x1, x2) =max{2x1, 3x2}