[jb9]

It's 7 outs for the turn, but if you don't get the fullhouse or 4 of a kind on the turn, you will then have 10 outs for the river.

You have 33, and the flop is 3T9, and, as you note, you have 7 outs (one 3, three Ts, three 9s,).

If the turn is not a 3, T, or 9, you will have 3 more outs (the 3 cards that pair that card).

So, if the turn is a King, you can make a full house or quads on the river with:

1 three
3 tens
3 nines
3 kings
-------
10 outs