Four numbers are written in a row. The average of the first two is 21, the average of the middle two is 26, and the average of the last two is 30. What is the average of the first and last of the numbers?<spanclass=′latex−bold′>(A)</span>24<spanclass=′latex−bold′>(B)</span>25<spanclass=′latex−bold′>(C)</span>26<spanclass=′latex−bold′>(D)</span>27<spanclass=′latex−bold′>(E)</span>28