Algebra
posted by Rene .
Solve for n
á = (n2) * 180 / n = 180 – 360/n

Although you do not need to know this to answer that question, that is the formula for each internal angle (a) of a regular polygon with n sides.
360/n = 180a
n = 360/(180a)
n = 4 for a = 90 degrees (a square) etc.