The gas mileage of a subcompact car is given by m = -0.04x² + 3.6x - 49, where x = the speed in miles per hour and m is given in miles per gallon.

a) What is the gas mileage for a speed of 25 miles per hour?

b) At what speed(s) would the gas mileage be 31 miles per gallon?

c) Will the vertex of this parabola be a maximum or a minimum?

d) Find the vertex of this parabola and write a sentence interpreting each of its coordinates.