. . .Thank you. So the answer is 5.
Yes, but only so long as the entire 10 BTC balance at address A in the beginning of this process was all received in a single previous transaction.
Here is another example:
Prior to Block B, I receive 2 separate transactions (Ta and Tb) at address A for 5 BTC each.
As of block B my address A has a balance of 10 BTC.
I decide to spend some of it so my client generates and broadcasts a transaction (T1) using one of these 5 BTC previous outputs (Tb) as an input with a 1 BTC output to destination address D and 4 BTC to change address C. At approximately the same time someone else broadcasts a transaction (T2) with a 5 BTC output to address A.
The miner which ultimate solves (B+1) includes T2 in the block but not T1 because it saw T2 first and had already started working on the block before T1 arrived.
T2 gets included in (B+1). T1 gets included in (B+2).
As of (B+3) what is the balance of address A?
In this case the balance of address A is 10 BTC. (Consisting of 2 separate 5 BTC outputs)
The balance of address B is 1 BTC
The balance of address C is 4 BTC
