Answer:
If the mother (red line) cycles at 12 mph, it means that in half an hour (x=0.5) she cycled for 6 miles.
The daughter (blue line) walks at 1/3 of her speed, or 4 mph. It means that in half an hour she traveled 2 miles, and 4 miles after an hour.
Assuming that they start at the same point at distance zero, it's just joining the dots.
