we know that each angle in a regular polygon is given by the formula
angle=(180)(n-2)/n where is number of sides
we actually have the angle, so we can write
156=(180)(n-2)/n
156*n=180 *(n-2)
furthermore
156n=180n-360
360=180n-156n
360=24n
n=360/24
n=15
this is a polygon with 15 sides