Penalty Spot on a Run play by A...

[new_official_11]

1st play of the game the other night; we had A 1st and 10 on the A's 20-yard line. A runs to A's 29 but we had a Block in the back at the B 35-yard line. Do you penalize this from the A 35 to the B 25 or can you go to the end of the run to the A 19? Thanks

[GA Umpire]

1st play of the game the other night; we had A 1st and 10 on the A's 20-yard line. A runs to A's 29 but we had a Block in the back at the B 35-yard line. Do you penalize this from the A 35 to the B 25 or can you go to the end of the run to the A 19? Thanks

See 10-4-4 and 10-6. 
All-but-one.

[refjeff]

1st play of the game the other night; we had A 1st and 10 on the A's 20-yard line. A runs to A's 29 but we had a Block in the back at the B 35-yard line. Do you penalize this from the A 35 to the B 25 or can you go to the end of the run to the A 19? Thanks

Since the foul was in advance of the end of the play, the enforcement spot is the basic spot i.e., the end of the run.

You're confused on you A's and B's.  The play started on A's 20 and gained 9 yards to A's 29.  There was a BIB 6 yards in advance of the end of the run.  That's A's 35 yard line.  B's 35 yard line is still 30 yards away on the other side of the 50 yard line.