You do not receive 25k, it is allocated from the total budget. Before it is ever spent. Ok now one year later, we might have spent 20k on AWS than there is an expense of 20k on the left side of the balance sheet.
The reason it is called a balance sheet is because the expense and the income need to be equal. So, we write 20k in AWS credits on the right.
I recommend you read a bit about accounting than it might make a bit more sense.