I don't know how to solve this task:

Participants of math competition are solving six tasks. For each task

you can get one of marks - 6,5, 3 or 0 .

It transpired that for each pair of participants we can indicate two

tasks , that in each of them participant A got different mark from

participant B.

Delimit the highest number of participants for which this situation is

possible.

Could anybody help me?

Thanks in advance