Kaitlin deposits 400 into an account that pays simple interest at a rate of 2% per year how much interest will she be paid in the first 6 years

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?