Final answer:
The initial impact of Gilberto's deposit on First Main Street Bank's reserves is an increase by the amount he deposits, which in this scenario would be $1,500,000.
Step-by-step explanation:
When Gilberto makes a deposit to First Main Street Bank, the bank's reserves increase by the amount he deposits. Therefore, if Gilberto were to deposit $1,500,000, the bank's reserves would increase by this amount, assuming that the deposit goes into a reserve account and not directly into loans or investments. However, the example provided mentions a scenario where a bank has to maintain certain reserves, purchase bonds, and adjust loans to maintain its required reserve ratio.
If Gilberto's deposit affects the bank in a similar manner as the provided examples, the bank might have to make adjustments to its loans to ensure it meets reserve requirements. But the initial impact of the deposit alone, without considering subsequent transactions, is an increase in reserves.