4. A room has one door, two windows, and a built-in bookshelf and it needs to be painted. Suppose that one gallon of paint can paint 120 square feet. The length and width of the door is 9ft by 3.5ft. The length and width of the windows are 4ft by 3ft. The length and width of the book shelf is 9ft by 4 ft. The length, width, and height of the room is 20ft by 25ft by 20ft. Calculate and output the amount of paint needed to paint the walls of the room. Please solve the problem using Math, and step by step instructions on how you did it. The instructions should be in steps and not a paragraph. Mention all assumptions you may make, write down all the formula you used for the calculation and give your solution at the end with the right units. If you do not follow all the steps, and write all the details, you will not get full credit. (25 points)