O&M = Operations and Maintenance
a) I think it's just 5% not 5% minimum
b) You receive Retention Sum (=2) and Final Acceptance (=1) but equivalent to the limit they set
This is a legal question, and you should run this past a lawyer to get things clear. I am not a lawyer, but that is how I would read it. However, for legal advice, it's better to use a lawyer rather than a teacher.