A department store's customer parking lot has 4 rows with an equal number of parking spots in each row. The lot also has 15 parking spots for store employees. If c cars can be parked in each of the 4 main rows of the parking lot, what is the expression for the maximum number of cars that can be parked in the parking lot?
15c − 4
c(15 − 4)
4c + 15
4(c + 15)