A directly proportional relationship satisfies a proportion or two equal ratios. You can create a ratio between x and y coordinates written as y/x.
So when y = 32 and x= 20, the ratio is 32/20. If y = 40, what is x? This is the ratio 40/x. Set them equal in a proportion. Then cross multiply to solve for x.
$26.46 I divided 15.12 by 8 to get the cost of just one gallon , which was $1.89. 14 x 1.89 = 26.46, which would ideally be the cost to fill a 14-gallon tank.