7) The final cost , including tax, of buying a pair of jeans is $37.82. If the tax was 6.5%, what was the pre-tax cost of the jeans?

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?