How many sides are there on a convex polygon if the sum of the interior angles is 3240?

18

19

20

21

20

Step-by-step explanation:

Let the number of sides be n

One exterior angle = 360/n

Exterior angle + interior angle = 180

Interior angle = 180 - Exterior angle

= 180 - 360/n

Sum of interior angle = n (180 - 360/n) = 3240

n (180 - 360/n) = 3240

180n - 360 = 3240

180n = 3240 - 360

= 3600

n = 3600/180

= 20