Whenever Katie and her family eat donuts, they need some coffee to dunk them in. She notices that for each donut they need 2 ounces of coffee. Every pot of coffee she makes contains 12 ounces and costs $3 to make. If her family finishes 3 dozen donuts, how much do they spend on coffee?
Please reason step by step, and put your final answer within \boxed{}.
user