(1)
3(2a+1)+2(3-a)
=6a+3+6-2a
=6a-2a+9
=4a+9
(2)
3m-2n+［-4m-(3m-n)］+(m-3n)
=3m-2n+[-4m-3m+n]+m-3n
=3m-2n+[-7m+n]+m-3n
=3m-2n-7m+n+m-3n
=-3m-4n