Why did the development of the time zones make train schedules more reliable
a) time zones set the entire country to the same time
b) time zones measured time locally instead of country-wide
c) time zones made sure that each state was in only one zone
d) time zones created a standard of time that all trains follow

Time zones created a standard of time that all trains follow. Your welcome (:

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.