[(3a-4b)(-3a-4b)-(4b-3a)²-3a(1/3ab²+a-b)]÷(-3a)
=[(-4b+3a)(-4b-3a)-(4b-3a)²-3a(1/3ab²+a-b)]÷(-3a)
=[16b²-9a²-16b²+24ab-9a²-3a(1/3ab²+a-b)]÷(-3a)
=[24ab-18a²-3a(1/3ab²+a-b)]÷(-3a)
=6a-8b+1/3ab²+a-b
=7a-9b+1/3ab²