Factor the monomial completely 42a3b3

Me. i can't figure out this question. give an explanation too. .

Tomas used 3 1/3 cups of flour and now has 1 2/3cups left. which equation can he use to find f, the number of cups of flour he had to begin with? f+3 1/3=1 2/3 f-3 1/3=1 2/3 3 1/3f=1 2/3 f/3 1/3=1 2/3

State one method by which you can recognize a perfect square trinomial.