Answer: 13.7ft (1 decimal place)
Explanation:
For this question you will have to use Pythagoras theorem.
The formula for the short side is x²=c²-b² and when you put the numbers from this question into it you get x²=15²-6²
15²=225
6²=36
x²=225-36
x²=189
Then, as you want to find x on its own, you would have to square root 189 which is 13.7 (1 decimal place).
Hope this helps :)