Can anyone please help me? Due soon! Please and thank you.

Janet drove 300 miles in 4.5 hours. write an equation to find the rate at which she was traveling

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?

Which shows how to solve the equation 3/4x=6 for x in one step?