One advantage that Europeans had over Africans during the slave trade was...

Europeans' conquest of Africa. One overwhelming advantage was the Europeans' technological superiority. The Maxim gun, invented in 1884, was the world's first automatic machine gun. European countries quickly acquired the Maxim, while the resisting Africans were forced to rely on outdated weapons.

Use the formula: (n-2)×180, where n is the number of sides(18-2)×180= 28800, now this is the full exterior angle of 18-gon so you divide it by 18.28800÷18=160

I'm pretty sure that's called a volcano