Find each percent of change. Round to the nearest tenth if necessary. State whether the percent of change is an increase or a decrease. 18 students to 22 students

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?