Flag on loose ball plays

[foureyesallbad]

NFHS:

Situation 1:

Ball is on A's 40. A75 holds B90 at A's 36 on an incomplete pass. Do we assess from the previous spot (A's 40) or the spot of the foul (A's 36)?

Situation 2:

Ball is on A's 40. A47 catches a pass at the 50 and runs to B's 1, where he is tackled. However, A35 holds B20 at A's 6. Do we assess from the previous spot (A's 40), the spot of the foul (B's 6), or the end of the run (B's 1)?

Situation 3:

Ball is on A's 40. B97 is caled for roughing the passer at A's 36 on an completed pass which ends at A's 49. Is the roughing the passer penalty assessed to the end of the play or does A have to choose between the result of the play/roughing penalty?

Thanks in advance for anyone who can help. I have suddenly been thrust into a position where I'm having to white hat some youth football and I want to do a good job.

If you can offer justifications and rule citings that would be great too!

Thanks again.
4eyesallbad