You are saving up to buy a Toyota Tundra, which costs $35000 now. You don't think the price of the Toyota will change over the next two years. You don't want to borrow to pay any of this cost. You now have $10000 toward the Tundra and can save $850 per month. At what monthly interest rate can you save enough to buy the Toyota in 24 months? (Note: you will need a financial calculator to solve this problem.)