(a+b+8)^2-(a+b)^2-16(a+b-3)=
=a^2+b^2+64+2ab+16a+16b-(a+b)^2-16(a+b-3)
=a^2+b^2+64+2ab+16a+16b-(a^2+2ab+b^2)-16(a+b-3)
=a^2+b^2+64+2ab+16a+16b-(a^2+2ab+b^2)-16a-16b+48
=a^2+b^2+64+2ab+16b-(a^2+2ab+b^2)-16b+48
=a^2+b^2+64+2ab-(a^2+2ab+b^2)+48
=a^2+b^2+64+2ab-a^2-2ab-b^2+48
=b^2+64+2ab-2ab-b^2+48
=64+2ab-2ab+48
=64+48
=112
