4n-m 3m+n--------- ---------20mn² - 15m²n8----x-2 + x² + 2x + 4x-4y x+4y--------- -----------6x(x-y) - 6x(x+y)b+3 b-1------ -------9b-27 - b² - 3b

4n-m     3m+n     12mn-3m^2-12mn-4n^2     -3m^2-4n^2
---------    ---------= ---------------------------------- =------------------
20mn² - 15m²n             60m^2n^2                60m^2n^2



 8                         8+x^3-2x^2+2x^2-4x+4x-8             x^3                                     
----  + x² + 2x + 4=------------------------------------------------=--------
x-2                                   x-2                                  x-2

                                   
b+3      b-1           b+3         b-1             b^2+3b-9b+9         (b-3)^2          b-3
------    -------    =-------------- - ---------------= ---------------------=----------------------=---------
9b-27 - b² - 3b       9(b-3)        b(b-3)         9b(b-3)               9b(b-3)           9b