In the POH, it gave a sample problem where the headwind speed of 10 kts is subtracted from the predicted ground speed 109 kts (109-10 = 99kts) giving the new predicted ground speed (more like TAS) of 99 kts.
1). I think you're getting a little confused over speed titles but ending up with the right answers. Any wind component is applied to the True Airspeed to make a Ground Speed. Add tailwinds, subtract headwind components. TAS 100kts with a
tail wind of 15kts makes a G/S of 115kts
2). -3C is ISA minus eight. If the temp at 5k should be +5 you would interpolate between the ISA and minus ISA figures.
Maybe buy your instructor a coffee and a burger and have a friendly refresher on flight planning.
