[Risolto] Chi puo gentilmente aiutarmi? Grazie mille

$(6a-4b)(a+2b)-(2a-b)(5a+3b)+a(4a-7b)+6b^2=$

$=6a^2+12ab-4ab-8b^2-(10a^2+6ab-5ab-3b^2)+4a^2-7ab+6b^2=$

$=6a^2+12ab-4ab-8b^2-10a^2-6ab+5ab+3b^2+4a^2-7ab+6b^2=$

$=(6-10+4)a^2+(-8+3+6)b^2+(12-4-6+5-7)ab=$

$=b^2$