Can someone pls help me

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?

Which equation can be used to measure the density of water in a spherical water tank? let w represent the number of water particles within the region.

The perimeter of a quarter circle is 14.28 miles. what is the quarter circle's radius?