The word problem gives a rate of oil consumption at a rate of 25 gallons per 3 hours and 45 minutes. 3 hours and 45 minutes can be displayed as 3.75 hours. so you can say the generator consumes oil at a rate of 25 gallons per 3.75 hours. The following equation give you the oil consumption on a per hour basis; 25/3.75 and that gives you 6.67 gallons per hour. In 6 hours the generator will consume 40 gallons.