Sarah and John live 18 miles apart. They decide to meet at a coffee shop that is exactly halfway between their homes. Sarah starts walking from her house at a speed of 3 miles per hour, while John starts cycling from his house at a speed of 6 miles per hour. If they both leave their homes at the same time, how long will it take for them to meet at the coffee shop? Let's think step by step and output the final answer within \boxed{}.
user