ANSWER
(10/3 miles) / (1 hour)
EXPLANATION
A unit rate is a rate where the denominator is 1. In this problem, the denominator is the time in hours. If Rebekah walks 10 miles in 3 hours, we have to find how many miles will she walk in 1 hour,
[tex]1hour\cdot\frac{10miles}{3hours}=\frac{10}{3}miles[/tex]She will run 10/3 miles in 1 hour. Hence the unit rate is (10/3 miles) / (1 hour).