Julia own a coffee shop. she expermented with mixing city roast colombian coffee that cost $7.80 per pound with french roast colombian coffee that cost $8.10 per pound to make a 20 pound blend. her blend should cost her $7.92 per pound. how much of each tupe of coffee should she buy?

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?