What is mean by demos

:calculate the sum of the interior angles of a 13-sided polygon.

What structure on the south african coast has a range of 63 km and releases flashes every 30 seconds?

(10 points) 1. cone 2. rectangle 3. triangle 4. circle 5. cylinder a. perpendicular cross section of a pyramid b. perpendicular cross section of a cylinder c. parallel cross section of a sphere d. shape created when a rectangle is rotated about the y-axis e. shape created when a right triangle is rotated about the y-axis