The marginal cost (in dollars per square foot) of installing x square feet of kitchen countertop is given by C'(x) = x a) Find the cost of installing 55 ft of countertop. b) Find the cost of installing an extra 12 ft of countertop after 55 ft have already been installed. a) Set up the integral for the cost of installing 55 ft- of countertop. C(55) = dx 0 The cost of installing 55 ft of countertop is $ (Round to the nearest cent as needed.) b) Set up the integral for the cost of installing an extra 12 ft after 55 ft has already been installed