Simplify:(a)12a5b34a3b(b)a-a×b-a×c-aa-2a×b-2a×c-2a(c)rs2t3×r4s5t-6×r7s8t-9r10s11t-12×r13s-14t15(d)(16a2)12×(36a4)-122a12×5a32×8a94