A power line is to be constructed from a power station at point A to an island at point C, which is 2 mi directly out in the water from a point B on the shore. Point B is 8 mi downshore from the power station at A. It costs $4200 per mile to lay the power line under water and $3000 per mile to lay the line under ground. At what point S downshore from A should the line come to the shore in order to minimize cost? Note that S could very well be B or A. (Hint: The length of CS is StartRoot 4 plus x squared EndRoot.)