Whoa, Dudes.
Absolutely, this is not a case where the penalty may be added to the end of the last run, because, as Magician pointed out, there was no change of possession during the down (which was a major difference in interpretation between Adams and Redding some time back, but that's another story).
But let's step back a second.
-The foul occurred during the legal forward pass play portion of the down.
-The Basic Spot for fouls that occur during a legal forward pass play is the Previous Spot (10-2-2-d-3). That rule governs unless 10-2-2-e-1 can apply, but 10-2-2-e-1 doesn't apply, since there was not a change of possession during the down.
-So, by 10-2-2-d-3, the Basic Spot is the Previous Spot, and, by the 3 and 1 principle, Team B fouls are penalized from the Basic Spot, so the penalty (15 yards plus a first down) is enforced at the Previous Spot, which yields A, 1/10, B-30, PC=25, GC=Snap (due to the apparent touchback).
Robert