Final answer:
The sum of the interior angle measures of a polygon is found by using the formula (n-2) x 180 degrees, where n is the number of sides of the polygon. In this case, the polygon has 21 sides.
Step-by-step explanation:
The sum of the interior angle measures of a polygon can be found using the formula (n-2) x 180, where n represents the number of sides of the polygon.
In this case, we have (n-2) x 180 = 3420.
To find n, we can solve this equation:
(n-2) x 180 = 3420
n-2 = 3420/180
n-2 = 19
n = 19 + 2
n = 21
Therefore, the polygon has 21 sides.