Answer:
see attached
Explanation:
You want the possible lengths of the third side of a triangle with side lengths 20 m and 18 m.
Triangle inequality
If the third side is length c, the triangle inequality requires ...
18 +c > 20 ⇒ c > 2
20 +c > 18 ⇒ c > -2
18 +20 > c ⇒ c < 38
The possible lengths for the third side (c) are ...
2 < c < 38
That is, the third side must lie between the difference and the sum of the given sides.
The attachment shows the values on the list that are in this range.