Answer:
m∠3 = 78°
Explanation:
From the figure, we have a circle. Also, we have two lines AC and DB being these two lines diameters. A diameter is a line that passes through the center of the circle and touches it in two different points. We also know that m∠1 = 78° and given that angle 1 and angle 3 are opposite, they measure the same. Therefore m∠3 = m∠1 = 78°