Answer:
C. Ian rode less than 1 hour
Explanation:
It never hurts to think about what the problem statement is telling you. Ian rode at a speed that would take him 18 miles in 1 hour.
Interpretation
Clearly, Ian would pass the 15-mile mark in a 1-hour ride before an hour had elapsed. If he only rode 15 miles, he rode less than 1 hour.
The actual time Ian rode is given by the relation between speed, time, and distance.
time = distance/speed
time = (15 mi)/(18 mi/h) = (15/18) h = 5/6 h
Ian's riding time was 5/6 of an hour, which is less than 1 hour.