A power cable must be laid from a power plant to a new factory located across a shallow river. The river is45

45feet wide and the factory is180

180feet down stream and90

90feet from the bank. The cable costs540

540per foot to lay under water,90

90per foot to lay along the bank, and180

180per foot to lay from the bank to the factory. What path should be taken to minimize the cost and what is the minimum cost?