62. Business: increasing total cost. Kitchens-to-Please Contracting determines that the marginal cost, in dollars per square foot, of installing x square feet of kitchen countertop is given by C'(x) = 4x 1/3. a) Find the cost of installing 50 ft² of countertop. b) Find the cost of installing an extra 14 ft² of countertop after 50 ft² have already been installed.