Answer: it will take 4 more days before DeAndre finishes
Explanation:
DeAndre is 15 miles into a 51-mile backpacking trip in the wilderness. This means that he has already covered 15 miles and the total number of miles is 51. Number of miles left is 51 - 15 = 36 miles.
DeAndre can hike 9 miles per day. The number of days that it will take him to cover 36 miles would be 36/9 = 4 days