We know that each group of 5 miles takes 30 minutes, we need to find how many groups she hikes:
[tex]\frac{25}{5}=5[/tex]Then she hikes 5 groups of 5 miles.
Now we multiply this number of groups for the time it takes:
[tex]5\cdot30=150[/tex]Then it takes 150 minutes for the whole hike. Finally we divide this by 60 minutes (each hour is equal to 60 minutes):
[tex]\frac{150}{60}=2.5[/tex]Therefore it takes 2.5 hours to make the hike
