28 33 45 57 39 36 which of the numbers above could be subtracted from 84 without reagrouping?

The only number that could be subtracted from 84 without regrouping is 33.

This is because the rest of the numbers in the ones place are greater than 4 (in 84). Since they are greater than 4, you would have to borrow from the tens place/regroup.

The answer to this is 33