If \left|BC\right| \equal{} a, \left|AC\right| \equal{} b, \left|AB\right| \equal{} c, 3\angle A \plus{} \angle B \equal{} 180{}^\circ and 3a \equal{} 2c, then find b in terms of a.<spanclass=′latex−bold′>(A)</span>23a<spanclass=′latex−bold′>(B)</span>45a<spanclass=′latex−bold′>(C)</span>a2<spanclass=′latex−bold′>(D)</span>a3<spanclass=′latex−bold′>(E)</span>32a3