The exterior angles = 180 - 157.5 = 22.5 degrees
the exterior angles of all polygons add up to 360 degrees
therefore the total number of sides n = 360 / 22.5 = 16
I beleive the correct answer would be the either the second, or the last one, but you go with whatever feels more comfortable. Hope this was helpful! (:
Answer is 50cm, to get the diameter you divide the circumference by pi.