16. The charge, C, in dollars, to use an Internet service is a function of m, the number of months of use, and t, the total number of minutes on-line:
C=f(m,t)=35+15m+0.05t.
(a) Is f a linear function?
(b) Give units for the coefficients of m and t, and interpret them as charges.
(c) Interpret the intercept 35 as a charge.
(d) Find f(3,800) and interpret your answer.