a unit rate, in this case, would be how far each person could walk in 1 hour.
Max walks 5 mi/2 hrs, so divide 5 by 2 to get 2.5 miles/hour
Lisa walks 6 mi/3 hours, so divide to get 2 miles/hr
To find how far Max can walk in 3 hours, take his unit rate (2.5 mi/hr) and multiply by 3. To find how far Lisa can walk in 0.5 hours, take her unit rate (2 mi/hr) and multiply by 0.5.