The sum of interior angles formula is:
S = 180(n - 2)
In this case:
6840 = 180(n - 2)
Let's solve for n:
Divide both sides by 180:
38 = n - 2
Add 2:
n = 40
Therefore, this polygon is a 40-gon. If you want to be super cool, you could call it a tetracontagon.