Plsssss help with questions 13 and 14

Question

Thank you for your help. Here is a link to the problem: Link to image of problem

Answer 1

In the linked image, the length of arc BC is 80°, not 75°. That's because arc ABC is 180° and arc AB is given as 100°. For the same reason, arc CD is 70° not 75°.

For question 13, angle A is an inscribed angle subtending arc BC, and the measure of an inscribed angle is equal to 1/2 the measure of the arc it subtends.

For question 14, angles AXD and BXC are vertical angles formed by the two chords AC and BD. The angle measure of angles AXD and BXC are equal to 1/2 of the sum of the arcs that the two angles intersect (arc AD + arc BD).

Answer 2