The number of guests per month at a large resort is given in the table below, where f(x) is the number of guests, in hundreds, x months since the beginning of the year.

x 0 2 4 6 8 10
f(x) 10 15 18 19 18 15

use the data in the table to create the standard form of the function that models this situation, where a, b, and c are constants.