Quick
along the western coast of south america, an oceanic tectonic plate is subducting beneath a continental plate. a chain of volcanoes called a continental volcanic arc is forming as a result of this process. where is the volcanic arc located?
a.
on the boundary between the oceanic and continental plates
b.
partly on the continental plate and partly on the oceanic plate
c.
on the oceanic plate
d.
on the continental plate

I'm pretty sure there's a geometry rule for   anyways, if the triangle is equilateral, and the circle is circumscribed, the circle is outside of the triangle.  to find the area, you need the radius.  the radius should be a straight line from the center of the triangle to any of it's points.  draw lines from the center of the circle to each of the triangle points.  draw three more lines from the center to the middle of the sides of the triangle.  you should now have six separate 30-60-90 triangles inside of your original triangle. use your 30-60-90 rules to solve for the radius, then the circumference. 

Ibelieve it is the 2nd answer, create gardens on all rooftops. let me know if this .

Asmall closed hole formed in an outwash plain or moraine. forms when a  glacier retreats then remains stationary.