One angle is 360/n
We can use x as the angle and n as the number of sides.
nx=360
so lets do this,
(2n - 4 )*90 = 1260
2n - 4 = 1260 / 90
2n - 4 = 42 / 3
2n - 4 = 14
2n = 18
n = 9
x is equal to 360/9
x is equal to 40 degrees for each exterior angle
so the interior angle's measurement would be 140 degrees
So the polygon would have 9 sides, the answer is 9.
