rectangular tank

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

Problem 03
A rectangular trough is 10 ft long and 3 ft wide. Find how fast the surface rises, if water flows in at the rate of 12 ft³/min.