4. Blue Lake Marina sells a make of cruiser for $16,800. This regular selling price covers overhead of 15% of cost and a normal net profit of 10% of cost. The cruisers were marked with a price that allowed the marina to offer a 20% discount while still maintaining its regular gross profit. At the end of the boating season, the cruiser was marked down. The marina made an operating profit of $2,500 per cruiser at the new regular selling price. What was the rate of markdown?