Let C(x) represent the cost at producing x items and p(x) be the sale price per item if x items are sold. The prot P(x) of selling x items is P(x) =xp(x) - C(x) (revenue minus costs). The average prot per item when x items are sold is P(x)lx and the marginal prot is dP/dx. The marginal prot approximates the prot obtained by selling one more item given that x items have already been sold. Consider the following cost functions C and price functions p. Complete parts (a) through (d) below. 000 = - 0.0512 + 60x + 30, p(x) = 300, a = 500