The number of years since Lena graduated
from middle school can be represented by the
equation y = a - 12, where y is the
number of years and a is her age. Is the
relationship between the number of years
since Lena graduated and her age
proportional or nonproportional?

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?