13. The isosceles triangle EJF is one of an unknown number of isosceles triangles from the original arch. Each isosceles triangle had the same vertex angle as triangle EJF. The sum of the vertex angles equals 180°. (2 points, one for the correct equation, one for the correct solution.)

Let x = the number of isosceles triangles.

Fill in the equation with your answer from Q12 and solve for x.

___ • x = 180