A power station is on one side of a straight river which is five miles wide, and a factory is on the other side, 20 miles up-river. A power line is to be run from the power station, under the river to some point A, which is x miles upriver from P, and then over land to the factory (see Fig. 27). If it costs $80 per mile to run the line under water and $50 per mile to run it overland, estimate x, the point on the other side of the river where the power line comes out of the river, if the total cost of the power line is to be as small as possible (a sketch of the grap-or a table may be useful)
