The formula to solve the problem is S= 180(n-2). Your n is the
number that they give you which is 28. So you just put 28 into
where n is {180(28-2)} and solve it.
step 1 =180(n-2)
step 2 =180(28-2)
step 3 =180(26)
step 4 =4680
The answer is 4680.
Correct me if I am wrong... I hope that help