L. C.M of 4 and multiples of 4 and 8

Give the equations of two different lines that are perpendicular to the line 3x + 4y = 7.

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?

(60 points) explain this in detail