In the situation described, since angles \( A \), \( B \), \( C \), and \( D \) are formed by two intersecting lines, we note that:
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\( \angle A \) and \( \angle C \) are opposite angles, and thus they are equal: \[ m\angle A = m\angle C. \]
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\( \angle A \) and \( \angle B \) are adjacent angles, which means they add up to \( 180^\circ \): \[ m\angle A + m\angle B = 180^\circ. \]
Since we know that \( m\angle C = 75^\circ \): \[ m\angle A = m\angle C = 75^\circ. \]
Thus, the correct answer for \( m\angle A \) is \( 75^\circ \).
To confirm:
- \( m\angle B = 180^\circ - m\angle A = 180^\circ - 75^\circ = 105^\circ \).
- \( m\angle D \) would also equal \( m\angle B = 105^\circ \).
So, the final answer is:
75°.