Calculating the return on investment using financial leverage. suppose dave invested only 20,000 of his own money and borrowed 180,000 interest-free from his rich father. what was his return on investment?

His return on investment (ROI) is based solely on money from his pocket.
If the profit is x dollars, the ROI is x/20000.  Here Dave levered 10:1 with the help of his father.  
If he had invested totally with his own money, the ROI would be x/200000, a much less impressive number even though the profit is the same.

Step 1: 6x-10=1; step 2: 6x=11