Given that:
Emma drinks 2/3 cups of water for every mile she hikes.
Capacity of water bottle = 4 cups
To find:
The number of miles she can hike before her water runs out.
Solution:
According to the given information,

Multiply both sides by 3.

Divide both sides by 2.

It means, she need 1 cup water for every 3/2 miles.
Multiply both sides by 4.


Therefore, she can hike 6 miles before her water runs out.