从里往外算：=8ab-{4a-3[6ab+5ab+5a-5b-7a]-2}
=8ab-{4a-18ab-15ab-15a+15b+21a-2}
=8ab-4a+18ab+15ab+15a-15b-21a+2
=41ab-10a-15b+2
也不说给点悬赏!汗