13. A large group of 30 people attended a hockey game. Each person ordered a hot dog or a slice of pizza from the concession stand. Hot dogs cost $2.50 each and a slice of pizza costs
$3.25 each. If the total bill for these items was $81.75, how many of each type was purchased?

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?