The unknown angle a is 23°.
Solution:
Given image is a trapezoid.
In the trapezoid, opposite sides are parallel.
If two lines are parallel, then the corresponding angles are equal.
⇒ 67° + ∠a = 90°
Subtract 67 from both sides.
⇒ 67° + ∠a - 67° = 90° - 67°
⇒ ∠a = 23°
The unknown angle a is 23°.
