Question 864457
Certainly, if x is less than 18 we can construct a triangle.
For example, we could have a triangle with side lengths
of 8, 10 and 17.  With a ruler, use 1/4 inch = 1 unit
and you can sketch it out.

Could there be a triangle with side lengths 8, 10 and 19?
You will notice you cannot construct one.

Is it possible for the side marked x to have length 18?