The graph shows the number of gallons of white paint that were mixed with gallons of green paint in various different ratios:

The title is Mixing Paint. The horizontal axis label is Green Paint in gallons. The scale is 0 to 24 in increments of 3. The vertical axis label is White Paint in gallons. The scale is 0 to 72 in increments of 9. Plot points at the ordered pairs 3,9 and 6,18 and 9,27.

The number of gallons of white paint mixed with 1 gallon of green paint is .