Please help me with this homework

1-for what value of x is line a parallel to line b 2-for what value of x is line a parallel to line b

Write an equation for the function that includes the points (1,4/5) and (2,2/3)

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?