D
1) We need to remind ourselves of the Triangular inequality so that we can tackle this question:
[tex]a+b>c,b+c>a,c+a>b[/tex]
Simply put, the sum of two sides must be greater than one of their sides.
2) Note that we were told that two of those legs have the size of 6 and 9
So, we can write out this:
[tex]\begin{gathered} 6+s>9 \\ s>9-6 \\ s>3 \\ 6+9>s \\ s<15 \end{gathered}[/tex]
3) Therefore, we can see that 3
Thus, the answer is D
