Lucy drove to the mountains last weekend. There was heavy traffic on the way there, and the trip took 7 hours. When Lucy drove home, there was no traffic and the trip only took 5 hours. If her average rate was 18 miles per hour faster on the trip home, how far away does Lucy live from the mountains? PLS HELP ASAP

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?