PLEASE HELP

i cannot figure this out

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?

Varies inversely with x. if y=8.5 when x=-1 find x when y=-1

Which of the following represents the length of a diagonal of this trapezoid?