1. **Stating the problem:** We have a triangle with two marked angles: one is 81° and the other is $k$. The triangle has two pairs of equal sides, indicating it is an isosceles triangle with two equal angles. 2. **Formula and rules:** In any triangle, the sum of the interior angles is always 180°. 3. **Using the properties of isosceles triangles:** Since two sides are equal, the angles opposite those sides are equal. Given one angle is 81°, the angle $k$ must be equal to 81° because they are opposite the equal sides. 4. **Calculating the third angle:** Let the third angle be $x$. Using the angle sum property: $$81 + 81 + x = 180$$ 5. **Solving for $x$:** $$x = 180 - 81 - 81 = 18$$ 6. **Answer:** The value of $k$ is 81°, and the third angle is 18°. This means the triangle has angles 81°, 81°, and 18°.