Answer:
56
Explanation:
The submarine climbed 9m, so its depth is now 40m + 9m = 49m.
Then, it dove 14m, so its depth is now 49m - 14m = 35m.
Finally, it climbed 21m, so its depth is now 35m + 21m = 56m.
Therefore, the integer that represents the depth of the submarine after these changes is 56.