If the given triangle with perimeter of 27 is equilateral (i.e. all sides and angles are equal), then the length of each of the 3 sides is 9. However, since there is nothing else given (image, measure of one side, etc.), you can simply say that the length of each of two sides are such that their sum will be greater than the third side. This theorem should apply with any given two sides of the triangle such as the one given above.
