Question

The sum of the angle measures of a polygon with n sides is 1260. find n.

Answer 1

Knowing the interior angle sum formula is; 

180x(n-2)

180x(n-2)=1260 (solve for n here) 
180n-360=1260 
180n=1260+360
180n=1620 
n=1620/180 
n=9

Therefore, this polygon has 9 sides.

Hope I helped :)