Hi Mike,
There’s an awful lot of missing info in that question? I’ll guess that you have a railcard and that the Underground journey will involve zone 6 and be after 0930 rather than before 0630.
My best guess is that you won’t be capped in that scenario. The most you can pay on buses in one day is £4.65 and the off-peak zone 1-6 tube journey is £2.20 making a total of £6.85.
If you were to make more tube journeys, or travel once in the evening peak, then it would depend on how many of your chargeable (ie not hopper) bus journeys were before 0930. They would not count towards the off-peak cap but would be added on afterwards. Worst case would be three chargeable bus journeys before 0930 (difficult with the hopper) making £4.65 and enough tube journeys to reach £8.85 at which point the anytime daily cap of £13.50 would cap you just before the £8.90 off-peak cap could.
Take a look at the capping examples page.