Can't understand how '-a' is coming in '3a-a'

If b=ixāxi)+jx(āxji)+kx(āxk); then b can be simplified by (A) (C) (C) Ex. (B) 0 None of these (D) 2 b-ix(axi)+jx(āxi)+kx(axk) -a(1)-i(a)-a(0)-i(ia)-a(kR)-R(Ra) - 3ä -a - 2ä Sol. ( Throa i InitJOntora