To determine how much fencing the homeowner needs to buy, we first need to establish the dimensions of the garden.
Let the width of the garden be \( w \) feet. According to the problem, the length of the garden is \( w + 9 \) feet.
Now we can calculate the perimeter of the rectangle (the garden) using the formula for the perimeter \( P \) of a rectangle:
\[ P = 2 \times (\text{length} + \text{width}) \]
Substituting the expressions for length and width into the formula:
\[ P = 2 \times ((w + 9) + w) \]
This simplifies to:
\[ P = 2 \times (2w + 9) \]
Now, distributing the 2 gives:
\[ P = 4w + 18 \]
Therefore, the total amount of fencing needed is \( 4w + 18 \) feet.
To provide a specific numerical answer, we would need to know the value of \( w \) (the width). However, if the homeowner simply wants a formula based on the width she chooses, then she needs to buy \( 4w + 18 \) feet of fencing.