2) 11 (2x-3y)-(88x^2-160xy):4x=11 (2x-3y)-8x (11x-10y):4x=11(2x-3y)-2(11x-10y)=22x-33y-22x+20y=-13y
4) (6a^2 b-5a b^2):ab-3 (2a-5b)=ab (6a-5b):ab-6a+15b=6a-6a-5b+15b=10b
6) (9s^4+3s^3 t):2s^3-(s-3t)=3s^3 (3s+t):2s^3-s+3t=(9s+3t):2-s+3t=(7s+9t):2
