Help on this question

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?

What is the factor form of x^2-9x+14

Cd is the perpendicular bisector of both xy and st, and cy=20. find xy.