An oil refinery is located 1 km north of the north bank of a straight river that is 3 km wide. a pipeline is to be constructed from the refinery to storage tanks located on the south bank of the river 8 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 downriver from the refinery should the point p be located?