Can someone help me please please

Anyone? 15m is what percent of 60m; 3m; 30m; 1.5 km?

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 is the focus of a parabola with equation y2=4x