Billy Hill lives in an old wooden shack. The walls of his shack are made of simple

Billy Hill lives in an old wooden shack. The walls of his shack are made of simple wooden boards and the windows are made of thin pieces of glass. During the winter, Billy uses a fireplace to warm his shack, but a great deal of thermal energy escapes, making Billy feel cold constantly. Suggest 3 modifications that Billy could make to his shack to reduce the amount of thermal energy lost.