The Johnson family is preparing to vacation at a famous amusement park. The park offers a family ticket discount package for an unlimited number of rides and will charge an entry fee for each person in the family. The equation below represents the cost per person, c of x, as a function of the number of people in the family, x.
c of x = 120 over x. + 7.5
If each person in the Johnson family paid $17.50, how many people were in the family?