12aba-15ab-42ab-30ab*12=12*1\3*0.2-15*1\3*0.2-42*1\3*0.2-30*1\3*0.2*12=-26.73
3ab(4a-5b)-6a(7ab-5b^2)=12a^b-15ab^2-42a^2b+30ab^2=-30a^2b+15ab^2=ab*(-30a+15b)=
1/15*(-10+3)=-7/15
12aba-15ab-42ab-30ab*12=12*1\3*0.2-15*1\3*0.2-42*1\3*0.2-30*1\3*0.2*12=-26.73
3ab(4a-5b)-6a(7ab-5b^2)=12a^b-15ab^2-42a^2b+30ab^2=-30a^2b+15ab^2=ab*(-30a+15b)=
1/15*(-10+3)=-7/15