$\"\"$

Since $\"\"$ forms a right angle.

If the noncommon sides of two adjacent angles form a right angle, then the angles are complementary by complement theorem.

$\"\"$ (Definition of complementary theoerem)

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

$\"\"$ (Subtract 40 from each side) $\"\"$

The measure of $\"\"$ is 50.