20)(9x7-6x6-3x5+x4-5x3+4x2-x3)/(3x3-2x2+x-1)
21)(3a2-2ab+b2)/(a-2b)
22)(8a2-6ab+12b2)/(2a-3b)
23)(8x3-36x2y+54xy2-27y3)/(2x-3y)
24)(6x3+4x2y2-15xy-10y3)/(2x2-5y)