Answer:
Below in bold.
Explanation:
The formula for the number of degrees in a convex polygon of side length n is S = 180(n - 2)
Solving for n:
 n - 2 = S/180
and n = (S/180) + 2.
 1.  n = (900/180) + 2 = 5 + 2 = 7 . This is a heptagon.
 2. n = (1800/180) + 2 = 12. A duodecagon.
 3.  n = (2160/180) + 2 = 14 sided polygon.
4. n = (2520/180) + 2 = 16 sided polygon.
5. n =  (3420/180) + 2 = 21 sided polygon.