The Zhao Family's utility function is U(x, y) = 4 ln x + 11 In y, where • x = quantity of essential goods the family purchases per month. • y = quantity of luxury goods the family purchases per month. The average cost/unit of essential goods and luxury goods are • Cx = $10 • Cy = $80 respectively, and the family's monthly budget is B = $4800. The utility-maximizing quantity of essential goods for the Zhao Family is found by solving the equation ... a. 240 +0.875x = 0 b. 4/x - 1.375 / 60 - 0.125x = 0 c. 4 ln x + 11 ln(60 - 0.125x) = 0 d. 4/x + 11 / 60 - 0.125x =0