i don't understand this at all

What are the soultion(s) to the quadratic equation 40- x^2=0

Acylinder has volume 45π and radius 3. what is it’s height?

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?