Optimization Problem

[superhume]

What would be the approach for this problem:
A power house, P, is on one bank of a straight river 200m wide, and a factory, F, is on the other bank 400m downstream from P. The cable has to be taken across the river under water at a cost of $12.00/m. On land the cost is $6.00/m. What path should be chosen so the cost is minimized?

Any help would be much appreciated.