Down payment on car

Based on the current prices of a car that I would like to buy, how do I find out how much money I need to save each month so that in four years I would have enough money to make a down payment of 18% of the current estimated value. Let's say that I can save the money in an account that is getting 3.5% return. How do I create a worksheet that shows how much I have to save each month so that in three years the value of the account is 18% of the current estimated value of the car? How do I determine the monthly savings amount needed for the car of my choice?