A principal was buying T-shirts for his school's math club and found that the total cost
in dollars could be found by the function f(x) = 9x + 7, where x is the number of
members in the club. If there are at least 12 members on the team but not more than
16, then which of the following statements describes the function?
A. The value of x must be a whole number between 12 and 16 and the value of f(x)
must be a whole number between 9 and 7.
B. The value of x must be a whole number between 12 and 16 and the value of f(x)
must be a whole number between 115 and 151.
C. The value of x must be a whole number between 0 and 16 and the value of f(x) must
be a whole number between 0 and 151.
D. The values of x and f(x) must both be whole numbers between 7 and 9.