An engineer said he could finish a highway section in 3 days with his present supply of a certain type of machine. However, with 3 more of these machines the job could be done in 2 days. If the machines all work at the same rate, how many days would it take to do the job with one machine?
<spanclass=′latex−bold′>(A)</span>6<spanclass=′latex−bold′>(B)</span>12<spanclass=′latex−bold′>(C)</span>15<spanclass=′latex−bold′>(D)</span>18<spanclass=′latex−bold′>(E)</span>36