Ornithomimus stood about 6 feet tall and was the fastest dinosaur at a speed of about 50 mi/h. The largest dinosaur, Seismosaurus, was 20 times as tall. How tall was Seismosaurus? This is for math

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?