Let's employ the triangle inequality here.
If the sides were to form a triangle.
Then if 3x was the longest side, it must be less than the sum of 15 and 9, being the other 2 sides.
So;
If 3x was the shortest side, then 15 would be the longest side, and thus
3x plus 9 must be greater than 15,
So;
So, the range of values for which x must lie is;
[tex]2i.e
any values greater than 2 but less than 8.