Here's question....I do know the answer, I need to know the formula.
Hello Josh,
The formula is:
TAS = CAS/√Relative Density
1.225 kg per cubic metre being standard SL density, the relative density is: air density at altitude/1.225
Note the above does not include correction for compressibility which is generally considered insignificant at the lowish speed and altitude in your example. To correct for compressibility you would substitue Equivalent Airspeed for CAS in the formula. I lifted the formula straight from my RAF gorundschool notes. There is a similar formula in "Aerodynamics for Naval Aviators" which is freely available online if you search for it.