Suppose interest rates fall such that the average yield on rate$-$sensitive assets decreases by $15$ basis points and the average yield on rate$-$sensitive liabilities

decreases by $5$ basis points.

$($a$)$ Calculate the bank's CGAP and gap ratio.

$($b$)$ Assuming the bank does not change the composition of its balance sheet, calculate the resulting change in the bank's interest income, interest expense, and net interest income.