Solve the Problem $f ( x ) = \frac { 2 } { 3 } x + 92$

Solve the problem.
-A driver wants to gauge the fuel efficiency of her vehicle at speeds of 30 mph and above. She notices that traveling at an average speed of 40 mph results in a rating of 32 mpg, where as at an
Average speed of 50 mph, her car rates 17 mpg. Find a linear function f(x) = mx + b whose input is The number of minutes for a call and whose output is the corresponding cost for the call. Use the Function to model the gas mileage y for an average speed of x mph.

A) $f ( x ) = \frac { 2 } { 3 } x + 92$
B) $f ( x ) = - \frac { 3 } { 2 } x + 92$
C) $f ( x ) = - \frac { 3 } { 2 } x + 28$
D) $f ( x ) = \frac { 2 } { 3 } x + 28$