3ab-4ab+8ab-7ab+ab=______． 7x-(5x-5y)-y=______． 23a3bc2-15ab2c+8abc-24a3bc2-8abc=______． -7x2+6x+13x2-4x-5x2=______． 2y+(-2y+5)-(3y+2)＝______． 1.3/7 × 49/9 - 4/3 2.8/9 × 15/36 + 1/27 3.12× 5/...