So if the car used 2 1/6 gallons for the trip, and the car gets 30 miles per gallon, you can just multiply 2 1/6 gallons by 30 miles. (Think of it like 30 miles + 30 miles + 5 miles [since 5 is 1/6 of 30])
2 1/6 * 30 = 65
So the trip covered 65 miles.