6+ (-3) math is hard and i'm bad at it plz

Name each raycalculation tip: in ray "ab", a is the endpoint of the ray.

If you could answer these your a life saver

You are standing next to a really big circular lake. you want to measure the diameter of the lake, but you don't want to have to swim across with a measuring tape! you decide to walk around the perimeter of the lake and measure its circumference, and find that it's 400\pi\text{ m}400? m. what is the diameter dd of the lake?