An oil refinery is located on the north bank of a straight river that is 1 km wide. a pipeline is to be constructed from the refinery to storage tanks located on the south bank of the river 6 km east of the refinery. the cost of laying pipe is $500,000/km over land to a point p on the north bank and $1,000,000/km under the river to the tanks. to minimize the cost of the pipeline, how far from the refinery should p be located?