When a car's tire pressure is 30 pounds per square inch (psi), it averages 20.5 mpg of gasoline. if the tire pressure is increased to 35 psi, the car averages 21.1 mpg of gasoline.
answer parts a) through c).
a) if someone drives an average of 23,000 mi per year, how many gallons of gasoline will he save in a year by increasing his tire pressure from 30 to 35 psi?

b.) if gasoline costs $2.00 per gallon, how much will he save in a year?

c.) assume that there are about 140million cars in a country and that these changes are typical of each car, how many gallons of gasoline would be saved if all drivers increased their cars' tire pressure?