How to use Tasker to answer a private number, play an audio file to the caller and hang up? I would like Tasker to answer any private number (without the audio playing through my phone's speaker) and play an audio file (an MP3 that says, "this phone does not accept calls from private numbers") and then disconnect the call. 

Can someone help me set up a Tasker profile for this?
Very few, if any, devices supports playing sound directly to the phone (voice) call audio stream.

Try playing a sound in Tasker using the Play Ringtone action to the Voice call audio stream, to see if your device support it.