Apply PigeonHole principle.
value of n will be (3-1) + (4-1) + (6-1) + 1= 11
but here no option which is 11.
now lets try 2nd way.
it may possible that after completion of task processes don't want to release resource (Yes it is not written any where that processes must release resources after Execution) so we can think like this also.
To overcome this situation we have to allocate all required resources to each process at very stating. i.e. 3+4+6 = 13
13 satisfy both cases. so in worst it should be answer.