there are spreadsheets floating around the forums but I just use online calculators from time to time.
Online Conversion - Ohm's Law Calculator
In your case, for 1.5 ohms at 8.5 watts you're at 3.57 Volts (hmmm... hh357?) at 9.5 watts, 3.77 volts
To blow the hh357, you have to go past 11.2...