$\"\"$

Since $\"\"$ is an isosceles triangle, the angles opposite to congruent sides are congruent. $\"\"$ .

Let $\"\"$ .

$\"\"$ (Angle sum theory)

$\"\"$ (Substitute $\"\"$ )

$\"\"$ (Add $\"\"$ )

$\"\"$ (Subtract 18 from each side)

$\"\"$ (Divide each side by 2)

$\"\"$

The measure of $\"\"$ is 81.