If m∠ BAC = 60°, then m∠ DBC is also 60°.
In geometry, angles that are opposite to each other when two lines intersect are called vertical angles. Vertical angles are always congruent, which means they have the same measure.
In this case, angle BAC and angle DBC are vertical angles because they are formed by intersecting lines. Since m∠ BAC is given as 60°, it means that m∠ DBC, the vertical angle, must also be 60°.
Therefore, the measure of angle DBC is 60°.
So, the correct answer is A) 60°.