The treadmill starts on low, from time 0 to 15 minutes. Then at 15 the graph jumps up and stays up to 45, so for 30 minutes starting at t=15 the treadmill is on high. Then we're back down to low from 45 to 60, 15 minutes. Then it's off.
Answer: After 15 minutes she turned up to high for 30, then back down to low for 15 then off. [top right choice]