What Don and Jorge said. I would add, if it's your first roll, I would suggest you bracket a bit I normally rate tri-x at half the manufactuer's recommendation. there is a big difference in the tonal ranges of the printed pictures depending on if you are using tx400 or txp320. the tx400 give a long tonal range with good shadow detail and a very light gray instead of a brilliant white. txp gives a much stronger (bad word, i know) tonal range from deep black to brilliant white. with medium format, you can try both and see which you prefer.
d76 at 1:1 is a great starting developer for either tri-x.
Take care,
Tom