anyone else get the dome7w thanked u like idk whats with it its not even the real person, btw can ppl go on my profile and try and answer a question its rlly ez

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?