So in (b) you have 2 COP's, the interception by B and later the fumble recovery by A.
You also have 2 fouls during the play, the hold by B, and the PF/FM by A. B's foul occurred AFTER they got the ball, but A's foul occurred BEFORE they got the ball (back).
Since A has possession when the down ends, they have first choice of accept/decline the penalty on B. If they accept, double foul.
If they decline B's foul for the hold, they do not get to keep the ball, which they got with "dirty hands" due to the FM foul. Instead, we would go back to the enforcement spot for A's foul, enforce the penalty for the FM, and B would get the ball.
A's foul occurred during a running play, and the basic spot is the end of the run, which was the B-15. All fouls by the defense (A was on defense when they fouled) are enforced from the basic spot.
So in this scenario, you'd enforce the PF/FM 15 yards from the B-15. It would be B 1/10 @ B-30, clock on the snap.
Since A would rather replay the down than give B the ball, this scenario is moot.
