Let A={1....10} and let K=AxA. Define the relation R on K by ((x,y), (z,t)) ∈ R <===> x+y=z+t.

R induces a partition on K. For each cell of this partition give a representative as well as the cardinality of the cell.

I really need some help on this. What does it mean by "each cell of the partition"? What is the partition and what exactly is a cell?