Someone please please please please help I need help please

For f(x) = 3x+1 and g(x) = x2 - 6, find (g/f)(x)

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?

Factor the polynomial by its greatest common monomial factor.