Holding (NCAA Rules)

[Da Official]

Help me with enforcing offensive holding...

3rd and 10 from Team A 20 yd line: A1 holds B1 at the 35 yd line while A2 runs past A1 and B1. A2 gets tackled at the 50 yd line.

If Team B accepts the penalty where will the penalty be marked off from?

I'm trying to get a good understanding of where holding penalties are enforced from....as I was under the impression if the penalty occurs behind the LOS it's marked off from the LOS and if the penalty occurs beyond the LOS its marked off from the spot of the foul.

Thanks!