Algebra word problem

Question

the amount of water used to take a shower is directly proportional to the amount of time. a shower lasting 18 minutes requires 12 gallons of water. find the amount of water used in a shower lasting 6 minutes.

Answer 1

18 : 12 :: 6 : g    proportion

18g = (12)(6)

 

Or 

 

6 min is 1/3 of 18 minutes

4 gal is 1/3 of 12 gall