You use 6 gallons of water on 20 plants in your garden. at that rate, how much water will it take to water 30 plants?

9 because if you split the planta up into 10's, you would split the gallons into 3's. Thats 3 gallons per 10 plants

To do this, set up a proportion.  The proportion would be 6/20=x/30.  To do this, multiply 30 by 6.  This gives you 180. Now you want to divide 180 by 20. This gives you 9.  It would take 9 gallons of water to water 30 plants.