Help with derivative word problem...?

Question

If g (v) is the fuel efficiency, in miles per gallon, of a car going at v miles per hour, what is the practical meaning of the statement g ' (55)= - .54

Answer 1

g '(55) = dg/dv at v = 55 = -.54 says that if you drove at 56 mph the the number of gallons used would increase by .54.