How many pairs of positive integers (a,b) are there such that the roots of polynomial x2−ax−b are not greater than 5?<spanclass=′latex−bold′>(A)</span>40<spanclass=′latex−bold′>(B)</span>50<spanclass=′latex−bold′>(C)</span>65<spanclass=′latex−bold′>(D)</span>75<spanclass=′latex−bold′>(E)</span>None of the preceding