What is the sum of all interior angles of a regular hexagon?

What is the sum of all interior angles of a regular nonagon?

What is the sum of all interior angles of a regular polygon of $12$ sides?

What is the number of diagonals in a heptagon?

What is the number of diagonals in an octagon?

What is the number of diagonals in a polygon of $12$ sides?

Find the number of sides of a regular polygon whose each exterior angle measure: $40°$

Find the number of sides of a regular polygon whose each exterior angle measure: $36°$

Find the number of sides of a regular polygon whose each exterior angle measures: $72°$