For this to work the best, we should convert all of the units to gallons. Martha used 17% of 8 gallons which is the same as 0.17*8 or 1.36 gallons. Brett used 0.18 of the 8 gallons, meaning that he used 0.18*8 or 1.44 gallons. For Mike, we are given that he used 0.7 gallons, meaning that since 1.44 is greater than both 1.36 and 0.7, Brett used the most oil.
