Answer:
The polygon has 9 sides
Explanation:
We need to equate the given expression to the given value and solve for n.
The sum of the interior angles, s, in an n-sided polygon is given by the expression:

We want to use this formula, to calculate how many sides has a polygon if the sum of the interior angles is 1,260°.
We solve the following equation for n.

Divide through by 180 to get:


Add 2 to both sides to get:


Hence the polygon has 9 sides