what are these lights costing you?

You have a lighted driveway - there are 5 lamps with 3 fixtures per lamp - the manufacturer states use no more than a 100 watt bulb in each fixture.  At a utility company cost of $.12 per kW Hour what are these lights costing you?  Oh, and they are on a timer set to turn on at dark, and off at daybreak.

Please show work?