Okay, so the perimeter of something is the measurement all the way around the outside of it. For example, we would find the perimeter of the garden by taking a measuring tape and measuring all the way around the outside of it.
We know the width of the garden is 73 feet, so both sides of the width would be 146.
Now if we do 332-146 we get 186, and that would be the length sides added together, so 186÷2=93.
We can check that our answer is correct by adding them together. 93+93=186, and 73+73=146. 186+146=332, so we know our math is correct.
(And the first time I did this I made a mistake, which shows how important checking our work is!)
The length of the garden is 93.