Solution:
1. The down payment required is USD 15,000.
2. Darren has saved USD 9,000 so far.
3. To find the fraction of the down payment saved, use the formula:
\text{fraction saved} = \frac{\text{amount saved}}{\text{total down payment}}
4. Substitute the given values into the formula:
\text{fraction saved} = \frac{9000}{15000}
5. Simplify the fraction:
* \frac{9000}{15000} = \frac{9}{15}
* Continue simplifying by dividing both numerator and denominator by their greatest common divisor, which is 3:
* \frac{9}{15} = \frac{3}{5}
Thus, Darren has saved \frac{3}{5} of his down payment.