The zener suggestion isn't much better!, just like the voltage divider you should run it at 5 times the load current, so still have 180W of heat to get rid of (assuming you can find a zener of high enough wattage?).
The answer, as already suggested, is a SERIES regulator, and not a parallel one - but it's design really depends on what it's for?, which is still apparently a secret?.
BTW, the difference is 36W maximum dissipation, as opposed to 180W all the time!.