Need help with a math problem

Question

matthews truck can drive 420 miles on a 20 gallon tank of gas. If we assume using gas at a steady rate is the relationship between the amount of gas and the miles driven a proportional relationship? How do we know?

Answer 1

420/20 = 21 mpg

distance traveled = 21 times number of gallons

D = 21G

It's a direct relationship. D is proportional to G

and G is proportional to D

G = (1/21)D