?A water line is to be built from point P to point S and must pass through regions where construction costs differ (see figure). The cost per kilometer

A water line is to be built from point P to point S and must pass through regions where construction costs differ (see figure). The cost per kilometer (in dollars) is 3k from P to Q, 2k from Q to R, and k from R to S. Find x and y such that the total cost C will be minimized.