Since angles ∠1 and ∠2 are supplementary, their measures add up to 180 degrees. Given that \( m∠1 = 77° \) and letting \( m∠2 = x° \), the equation you would write to solve for \( m∠2 \) is:
\[ x° + 77° = 180° \]
So the correct response is:
x° + 77° = 180°