Yes,
Blues&twos, that's correct
Reviewing the associated algorithm might help for understanding on the original poster's part, i.e. -
SAT = RAT / (1 + .2 X Ct X M^2)
Where SAT = Static Air Temperature, RAT = Ram Air Temperature, Ct = Temperature coefficient (recovery factor) for your temperature measuring system, and M = Mach No.
For RAT = -48°C, RAT = 273.15 - 48 = 225.25°K
SAT = 225.15 / (1 + .2 X .85 X 0.49) = 207.84°K - 273.15 = -65.31°K
If your aircraft has a TAT system (100% recovery, or >99%), Ct =1, and you can dispense with the Ct input in finding SAT.
Regards,
Old Smokey