Supplementary angles are two angles whose measures add up to 180 degrees. Given that \( m∠b = 98° \), we can find \( m∠a \) by using the following equation:
\[ m∠a + m∠b = 180° \]
Substituting the value of \( m∠b \):
\[ m∠a + 98° = 180° \]
Now, subtract 98° from both sides:
\[ m∠a = 180° - 98° = 82° \]
So, the measure of angle \( a \) is \( 82° \).
The correct response is:
82°