application of differentiation

An offshore oil well must be connected by pipe to the refinery.The oil-well is 6km off shore.The refinery is on the coast,6 km from the nearest point of land to the oil well. It costs $S per km to lay pipe along the shore but U "times" as much per km to lay pipe underwater.The pipe may laid either straight to the refinery or to an intermediate point on the coast then along the coast.

a.Give the total cost as a function of the distance x between the point directly opposite the oil well and the place where the pipe comes ashore.