If a person does work under a contract but the work is partially done say about 75 but without the 25 of work which is incomplete the 75 is of no use should the person be compensated quantum meruit?

I am not a legal expert but I would expect that the contract would make this clear. If the contract employs the person by the hour/day then the number of hours/days worked would need to be payed. If the contract specifies payment on completion then no payment would be made until the final 25% of the agreed specification was delivered.

You need to take the contract to an attorney/lawyer to get a proper answer on this because it is the CONTRACT that matters. look at the link I will place blow