Alan learned a total of 10 appetizer recipes over the course of 2 weeks of culinary school. After how many weeks of culinary school will Alan know a total
of 15 appetizer recipes? Assume the relationship is directly proportional.

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?