7a-4(5,6b-10(3,7a-(1,8b+5(2,4a-5,3b)+6a)-7b)).

7a-4(5,6-10(3,7a-(1.8b+5(2.4a-5,3b)+6a)-7b))=7a-4(5,6b-10(-14,3a+17,7b))=7a-4(5,6b+143a-177b)=7a-4(-171,4b+143a)=7a+685,6b-572a=-565a+685,6b