A group of college students are going to a lake house for the weekend and plan on renting small cars and large cars to make the trip. Each small car can hold 4 people and each large car can hold 6 people. The students rented 4 times as many large cars as small cars, which altogether can hold 56 people. Write a system of equations that could be used to determine the number of small cars rented and the number of large cars rented. Define the variables that you use to write the system.