A tank open at the top is made of sheet iron 1 inch thick. The internal dimensions of the tank are 4ft. 8in. long ; 3ft. 6in. wide ; 4ft. 4in. deep. Find the weight of the tank when empty and find the weight when full of salt water.(salt water weighs 64 lbs/ft³ and iron is 7.2 times as heavy as salt water).