IF THIS WRONG I FAIL!!!!

Matt has started a car washing business to save money for college. Each week, he
washes 3 more cars than he did the week before.
Part A: Matt started by washing 6 cars his first week in business. Write an explicit formula that can be used to find the number of cars he washed on any given week.
Part B: Part B: How many cars will Matt wash on his 11th week in business?