Fastest way to figure out redraw pot odds

Fairly simple, Hero has some kind of draw, villian has some kind of hand, but when hero makes draw, villian has redraws. How do you work out the redraw math and work it into the total percentage of hero making a hand that is good?

EG: Hero has 56h. Villian has TT. Flop is T 4 7 w/ 2 hearts. Hero has 15 outs twice, which makes him about a 55% in the hand. Villian has a 10 out redraw on the river for two cards however, which will be 20%ish to hit. I know its 42 / 58 from the card player odds thing, but i'd like to know how to work this out quickly.