Rachel carson's book silent spring, published in the 1960s,

Rachel carson's book silent spring, published in the 1960s awakened the American public to negative effects of artificial hormones and industrial chemicals.
The book was a documentary created to see the chemical usage of several agricultural companies. It discovered the negative effect of pesticides for the Environment

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