How can I solve this question step by step?

In the interior angles of a regular polygon sum to 1260 degrees. how many sides does it have?

9

Step-by-step explanation:

The sum of the interior angles of a polygon is

sum = 180° (n - 2) ← n is the number of sides, thus

180 (n - 2) = 1260 (divide both sides by 180)

n - 2 = 7 (add 2 to both sides)

n = 9

The number of sides of the regular polygon is 9