2a+3b-4+(-5a)-4b+5=2a+3b-4-5a-4b+5=-3a-b+1
2x+(4x+3y)-5+4y=2x+4x+3y-5+4y=6x+7y-5
5a(2a+3b-4)+4a-a^2=10a^2+15ab-20a+4a-a^2=9a^2+15ab-16a
2m-(3-4n+7m)-(-m+3n)= 2m-3+4n-7m+m-3n=-4m+n-3
\frac{1}{2}(6x-8y)-\frac{1}{3}(6y-12x)=\frac{1}{2}*2*(3x-4y)-\frac{1}{3}*3*(2y-4x)=3x-4y-(2y-4x)=3x-4y-2y+4x=7x-6y