Lots of good replies but I think your "depending on how I feel" is the best answer.
Daniel's numbers aren't bad but they are really too hard for an undertrained HS kid who might be running two races on top of his training.
85% would be ok, sometimes, but if you ran your 16:20 on a hilly, grass covered XC course and you do your tempo on the road during a week without a race it could be too slow.
You have to take everything into account to get the right pace.
One way to find the pace is to start at the slowest suggested pace here, say 6:15. Then run the next mile a little faster, maybe 6:08. Then a little faster, call it 5:58. If at the end of the 3rd mile, if you feel like speeding up, DON"T, just run a fourth mile again at 5:58. Your 3 mile tempo is then at 6:01 pace with a 6:15 warmup.
Next time you might start at 6:05, then 5:55 and 5:45. If you don't feel good enough to want to run a 5:35, you found your tempo pace for the day, 5:55. If you don't end up adding the fourth mile, do not increase the pace on the next tempo run. If you can't run your mile times so that each is faster than the last, slow down until you can.