It would be greatly appreciated if someone could .

B: 15

Step-by-step explanation:

You can get this answer using the pythagorean theorem.  a^2 + b^2 = c^2

In this case, you can assume a = 9 and b = 12 (though either or would still equal 15)

√9^2+12^2 = 15

The base of the box's length would be 15 feet long.  

B is 15 I got it by Pythagorean theorems

hope this .

r3t40