Give the step-by-step reasoning process and then the final answer. Janet has to drive 30 miles east from home to see her dermatologist and 50 miles west from home to see her gynecologist. If she has appointments with both doctors on the same day, how many gallons of gas does she use driving to both appointments and back home again, if her car gets 20 miles per gallon?
First find the total distance she drives to get to the dermatologist and back to her house: 30 miles * 2 = 60 miles. Then find the total distance she drives to get to the gynecologist and back to her house: 50 miles * 2 = 100 miles. Then add those two amounts to find how far she drives total: 60 miles + 100 miles = 160 miles. Then divide that distance by her car's gas mileage to find how many gallons of gas she needs: 160 miles / 20 miles / gallon = 8 gallons.
The final answer: 8.