Natural-gas rates. Table 1 shows the rates for natural gas charged by the Middle Tennessee Natural Gas Utility District during summer months. The base charge is a fixed monthly charge, independent of the amount of gas used per month. Table 1 Summer (May-September) Base charge $5.00 First 50 therms 0.63 per therm Over 50 therms 0.45 per therm (A) Write a piecewise definition of the monthly charge S(x) for a customer who uses x therms* in a summer month. (B) Graph S(x). (C) Is S(x) continuous at x = 50? Explain