11 the equation y= −0.0088x2+ 0.79x + 15 models the speed x (in miles per hour) and average gas mileage y (in miles per gallon) for a vehicle. what is the best approximate for the average gas mileage at a speed of 60 miles per hour? a) 15.7 mi/galb) 30.7 mi/galc) 61.9 mi/gald) 62.9 mi/gal

The first thing to do in this case is to replace the value of x = 60 in the given function to obtain the average fuel mileage in miles per gallon.
 We then have to replace:
 y = -0.0088 * x ^ 2 + 0.79 * x + 15
 y = -0.0088 * (60) ^ 2 + 0.79 * (60) + 15
 y = 30.7 mi / gal
 answer
 the best approximate for the average gas mileage at a speed of 60 miles per hour is
 B) 30.7 mi / gal