What is the size(in degrees) of each exterior angle in a convex polygon with $15$ sides?

Explain why $x=y$ in the following figure:

Explain why $x=y$ in the following figure:

On the line $AB$, at point $A$, measure and draw angle $BAC,$ a $75°$ angle.

Measure the line and construct $AB$ the same length in your book using a ruler and compass.

At point $B$, measure and draw angle $ABD,$ an angle of $125°$

A regular polygon has an interior angle of $172°$.

Find the number of sides of this polygon.