The total weight of the cargo entering a seaport each year can be modeled by the function C(t) 0.2t 3 1000t 2 10t 50,000, where t is the number of years since the port was opened. The average weight of cargo delivered by each ship is modeled by the function A(t) 0.1t 500. Write an expression describing the number of ships entering the port each year.