I need help please and thank you!

Prove that (x-2)is factor of p (x)=2x³-3x²-17x+30

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?

Find solution of the linear equation y = 2/3x + 1/3