The volume of a hot air balloon is 0.5x^3-2.3x^2-0.2x m^3. A second hot air balloon has a volume of 0.8x^3+1.1x^2+3.1 m^3. How many cubic meters greater is the volume of the second air balloon than the first?

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?