If 7 more boys join the Waverly Waves, how many girls should be added to the team in order to maintain the same ratio of boys to girls? Justify your answer.

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?