a)
[tex](3x-1)(2-x)-(2-3x)(x+1)=6x-3x^{2} -2+x-(2x+2-3x^{2} -3x)=6x-3x^{2} -2+x-(-x+2-3x^{2} )=6x-3x^{2} -2+x+x-2+3x^{2} =8x-4[/tex]
b)
[tex](3m+2n)(n+3m-1)+(m+2n-1)(3n-6m)=3mn+9m^{2}-3m+2n^{2}+6mn-2n+3mn-6m^{2}+6n^{2}-12mn-3n+6m=0+3m^{2}+3m+8n^{2}-5n=3m^{2}+3m+8n^{2}-5n[/tex]