Find the sum of all possible values of f(2) such that
f(x)f(y)−f(xy)=xy+yx, for every positive real numbers x,y<spanclass=′latex−bold′>(A)</span>25<spanclass=′latex−bold′>(B)</span>−45<spanclass=′latex−bold′>(C)</span>45<spanclass=′latex−bold′>(D)</span>23<spanclass=′latex−bold′>(E)</span>None