Answer to three friends each create 4 bags of starter bread dough. after ten days, each of those four bags is then divided into four more bags of dough. how many days pass before 192 bags of dough are created

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?