Assuming that the block in the back occurs during the run by B33:
Two fouls by team A. Illegal forward pass by B22 at B-11. Block in the back by B20 at B-30, end of the related run is B-25.
Team A has three options. They may decline both fouls, but they won't. Accepting the illegal forward pass foul results in 1st and 10 for team B at B-6. Accepting the block in the back results in 1st and 10 for team B at B-15. Team A will accept the illegal forward pass foul (don't even give them any options as the enforcement is obvious, unless time expires during the down).
If the block in the back occurs during the run by B22, then team A will accept that foul, 1st and 10 for team B at B-5.5.
The forward pass aspect is reviewable in NCAA under rule 12-3-2-d.