The equation z(z+i)(z+3i)=2002i has a zero of the form a+bi, where a and b are positive real numbers. Find a.<spanclass=′latex−bold′>(A)</span>118<spanclass=′latex−bold′>(B)</span>210<spanclass=′latex−bold′>(C)</span>2210<spanclass=′latex−bold′>(D)</span>2002<spanclass=′latex−bold′>(E)</span>1002