Your parents start saving for your sisters college education. She will begin college at the age of 18 and will need $4,000 per year at the end of each of the following four years she stays in college. Tuitions are paid after starting college. They will start to make a deposit one year from today in an account which pays 6% compounded annually and they continue making an identical deposit until the year your sister starts college. If a deposit of $1,987 will allow them to reach their goal, how old is your sister?