From the statement of the first problem, we know that:
0. the canteen holds 48 oz of water,
,
1. the hiker drinks 4 oz per 3/4 of a mile.
From point 2, we can compute the ratio of miles that the hiker does per oz water that he drinks:

Now, if we multiply the ratio by the amount of water that the hiker has, we get the number of miles that he can walk:

Answer
The hiker can walk 9 miles before running out of water.