Let a,b be integers greater than 1. What is the largest n which cannot be written in the form n \equal{} 7a \plus{} 5b ? <spanclass=′latex−bold′>(A)</span>82<spanclass=′latex−bold′>(B)</span>47<spanclass=′latex−bold′>(C)</span>45<spanclass=′latex−bold′>(D)</span>42<spanclass=′latex−bold′>(E)</span>None