We are told a carpenter trims a triangular peak of a house with three $7$ -ft pieces of molding. Also, the carpenter uses $21$ ft of molding to trim a second triangular peak. We are asked whether the two triangles formed are congruent. To answer the question, we will organize the given information using a table.

	First triangle	Second triangle
Information about the sides	Since the carpenter uses three $7$ -ft pieces of molding, we know the perimeter of the triangle is $21$ ft. We do not have further information about the sides.	Since the carpenter uses $21$ ft of molding, we know the perimeter of the triangle is $21$ ft. We do not have further information about the sides.
Information about the angles	No information about the angles is given.	No information about the angles is given.

Let's see now if we can use SSS or SAS to prove the triangles are congruent.

Although both triangles have the same perimeter, the sides of one triangle are not necessarily congruent to the sides of the other triangle. Therefore, we cannot use SSS to prove the triangles are congruent.
No information about the angles is given and thus we cannot use SAS.

Hence, we do not know if the triangles are congruent.

Exercise