So a dishwasher uses 444 gallons of water per load.
That means it'll use 444*215215215 = 95555555460 gallons of water for 215215215 loads
Since washing dishes by hand takes 666 as much as water in comparison to using a dishwasher, we can do 95555555460x666 to find that you need 6.36399999×10^13 gallons of water to wash 215215215 loads.
The question asks for how much more water in gallons you can save, so do 6.36399999×10^13 - 95555555460 to get 6.35444444×10^13 gallons
