Triangle ABC has side lengths in arithmetic progression, and the smallest side has length 6. If the triangle has an angle of 120∘, what is the area of ABC?<spanclass=′latex−bold′>(A)</span>123<spanclass=′latex−bold′>(B)</span>86<spanclass=′latex−bold′>(C)</span>142<spanclass=′latex−bold′>(D)</span>202<spanclass=′latex−bold′>(E)</span>153