2-28. According to the U.S. Department of the Interior, the amount of energy lost because of poorly insulated homes is equivalent to 2 million barrels of oil per day. In 2009, this is more oil than the United States imports from Saudi Arabia each day. If we were to insulate our homes as determined by Example 2-7, we could eliminate our oil dependence on Saudi Arabia. If the cost of electricity increases to $0.15 per kWh and the cost of insulation quadruples, how much insulation should be chosen in Example 2-7? (2.3)