You can
put this solution on YOUR website!You can start with the formula for the measure of an interior (vertex) angle of a regular polygon of n sides.
A.

Multiply both sides by n.

Add 360 to both sides.

Subtract 150n from both sides.

Divide both sides by 30.

The regular polygon has twelve sides.
B. Similarly:

Multiply both sides by n.

Add 360 to both sides.

Subtract 156n from both sides.

Divide both sides by 24.

The regular polygon has fifteen sides.
C. and D. Follow the same procedure as for A. and B.