HELP ME PLEASE

Given f(x)= 9x+1 and g(x)=x^3, choose the expression (f*g)(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?

How do i find the missing angle measure in a polygon