Question

find the measure of the missing angle.

Explanation:

Step1: Recall linear - pair property

Two angles that form a linear - pair add up to 180°.
Let the missing angle be \(a\) and the given angle be 21°. Then \(a + 21^{\circ}=180^{\circ}\).

Step2: Solve for \(a\)

Subtract 21° from both sides of the equation: \(a=180^{\circ}- 21^{\circ}\).
\(a = 159^{\circ}\)

Answer:

\(159^{\circ}\)