You commented that part of the instruction included "If the theorem cannot be applied, explain the reason."
The theorem cannot be applied. Since this is not a right triangle, we cannot solve using the Pythagorean Theorem unless we are given a height. If we have the height of this triangle, then we can break it into two different right triangles and solve.
What is a right triangle? A right triangle is a triangle that has an angle measurement of 90 degrees.
In summary, this is an isosceles triangle and the Pythagorean Theorem only applies to right triangles.