Question

A horse drinks about 120 gallons of water every four days at this rate about how many gallons of water does a horse drink in 28 days

Answer 1

840 gallons of water

Answer 2

First you want to divide 28 by 4, because it's counting in 4 day intervals and this will narrow it down to the average days.  This gives you 7, which you now multiply by 120, which gives you a total of 840 gallons within a period of 28 days.