First, you will need a knowledge of fractions. I'm sure you do.
Now, search up how many feet are in a single yard. I Googled it and I got 1 yard = 3 feet.
Now let's make a fraction out of that. 1 yard / 3 feet.
You can do 3 feet / 1 yard if you want to. They are both equal to each other.
Now we need to convert the 84 yards into a fraction.
Simply make the 84 yards over 1. 84 yards / 1.
Now we need to multiply these two fractions in a way that will cancel out the yards unit and leave us with only the feet units.
84 yards/1 * 3 feet/1 yard
The reason why I switched from using 1 yard/3 feet to 3 feet/1 yard is because in that setup the yards unit would cancel and leave us only with the feet units.
