on a trip , a cyclist averaged 12 miles per hour for the first 18 miles and 10 miles per hour for the remaining 18 miles . if the cyclist returned immediately via the same route and took a total of 7.3 hours for the round trip , what was the average speed ( in miles per hour ) for the return trip ?
"the time to go 36 miles was 18 / 12 + 18 / 10 = 1.5 + 1.8 = 3.3 hours . the average speed for the return trip was 36 miles / 4 hours = 9 mph . the answer is d ."
divide(add(18, 18), subtract(7.3, add(divide(18, 12), divide(18, 10))))