A lighthouse L is located on a small island 5km north of a point A on a straight east-west shoreline.A cable is to be laid from L to point B on the shoreline 10km east of A.The cable will be laid through the water in a straight line from L to point C on the shoreline between A and B, and from there to B along the shoreline.The part of the cable lying in the water costs $5,000/km, and the part along the shoreline costs $3,000/km. Where should C be chosen to minimize the total cost of the cable?