There are 6 sides so that means that the angles add to 180(6-2) = 180(4) = 720 degrees
So let's add up the angles and set that result equal to 720. Then solve for n
Note: I'm starting at the angle n and working counter-clockwise
(n)+(140)+(151)+(62)+(135)+(n+6) = 720
n+140+151+62+135+n+6 = 720
2n+494 = 720
2n+494-494 = 720-494
2n = 226
2n/2 = 226/2
n = 113
So the final answer is n = 113
