Franklin is throwing a pool party to kick off the summer. His pool is empty, so he starts filling it with water from a garden hose. There is a proportional relationship between the time Franklin has been filling up the pool (in minutes), x, and the volume of water in the pool (in gallons), y.

x (minutes) y (gallons)

1 18

2 36

4 72

5 90

Write an equation for the relationship between x and y. Simplify any fractions.

y=