(10 marks) A phone company is laying wire to connect two subdivisions, A and B, that lie on opposite sides of an 80m-wide river. Subdivision A lies on the north bank of the river at a point 900m west of subdivision B. It costs $50/m to lay the wire underground and $90/m to lay the wire underwater. Determine the path that the company must take to lay the wire so that the cost is at a minimum. Include a diagram.