Answer
See the explanation
Work Step by Step
To achieve a final balance of 100USD:
1. Transaction 1: Withdraw 100USD (resulting in a balance of 100USD).
2. Transaction 2: Add 100USD (no effect as the balance is already 100USD).
To achieve a final balance of 300USD:
1. Transaction 2: Add 100USD (resulting in a balance of 300USD).
2. Transaction 1: Withdraw 100USD (no effect as the balance is still 300USD).
So we have:
T1 reads → T2 reads → T2 writes → T1 writes $\$300$ (T1 overwrites T2)
T1 reads → T2 reads → T1 writes → T2 writes $\$100$ (T2 overwrites T1)
