The amount of heat transferred per hour through a glass window varies jointly with the surface area of the window and the difference in temperature between the areas separated by the glass. A window with the surface area of 7.5 square feet lose 135 BTU per hour when the temperature difference is 40 degrees Fahrenheit. How much heat is lost per hour for a similar window with a surface area of 12 square feet when the temperature difference is 35 degrees fahrenheit?