A natural gas plant is located on the north bank of a river that is 4 km wide. A pipeline will be laid from the natural gas plant to a distribution station. This station stands on the opposite bank of the river, 6 km west of the natural gas plant. The cost of laying a pipe over land to point A on the north bank is $30,000/km. It costs $75,000/km to lay a pipe under the river to the station on the opposite bank. How far should point A be located from the distribution station to minimize the cost of laying the pipeline?