Positive real numbers x and y satisfy y3=x2 and (y−x)2=4y2. What is x+y?<spanclass=′latex−bold′>(A)</span>12<spanclass=′latex−bold′>(B)</span>18<spanclass=′latex−bold′>(C)</span>24<spanclass=′latex−bold′>(D)</span>36<spanclass=′latex−bold′>(E)</span>42