Okay. So, there will be 12 small turbines, with 3 blades on each of them. 12 * 3 is 36. Marco will need 36 wind turbine blades total. 4 of them cost $79.64. 36/4 = 9. We would multiply 79.64 by 9 to get the cost for all blades. 79.64 * 9 is 716.76. The total cost for 36 blades would be $716.76.