The function f(x) = 1.50x + 12.50 relates how much kelsey pays for digital service, f(x), to the number of movies, x, she streams in a month. what is the value and meaning of f(18)?
a. $27.00; this is the amount kelsey pays for 18 months of service
b. $27.00; this is the amount kelsey pays for 18 movies in 1 month
c. $39.50; this is the amount kelsey pays for 18 months of service
d. $39.50; this is the amount kelsey pays for 18 movies in 1 month