PRSI monthly exemption and crossing the income ceiling

[deadlyduck]

Hi,
I know that this topic has been covered a lot in this forum so apologies if I've missed an answer to the following query:

Scenario:
Paid monthly, class A1 for PRSI, exemption €551
Cumulative reckonable pay at end of month 6 = 46300
Reckonable pay in month 7 = 4000
Cumulative reckonable pay at end of month 7 = 50300

Query:
When calculating the PRSI for month 7, does this person receive:

1. the full €551 monthly PRSI exemption amount;
2. only €300 of this (ie Ceiling less Cumulative Pay at end of month 6)
3. Nil, as the cumulative reckonable pay at end of month 7 is now in excess of the ceiling

All help would be gratefully received!