This divides our planet into the northern hemisphere & the southern hemisphere

The equator is what divides our planet into the Northern Hemisphere & the Southern Hemisphere. 

The equator Divides The Earth Into 2 Hemispheres It Is Also Called The 0Degree Latitude

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. 

Assuming this is a question on a test just name a restaurant by your house and the state you live in, its not too difficult : )