I wanted to check if the method I used to solve this question is right, or if I just got lucky with the answer. Greg solved this using triangles and the property that the 3rd side should be less than the sum of the other 2 sides.

What I used is -

**Any figure has the most efficient (maximum) perimeter and area when it’s a regular figure.**- In the given figure, the maximum side given is 5.
- This means, that when the pentagon is regular, all sides would be 5 and the
**perimeter is 25**. - Since the sides are different in the given figure, it’s
**not a regular pentagon.**Hence, the perimeter should be less than 25. - The sum of the given sides is 14, so the unknown side should be 5 or 10, since 15 would result in a perimeter of 14+15 = 29 which is greater than the perimeter of the regular pentagon, which is 25.

So I went with option C. Is this the right logic to apply to this problem?