Net interest income = Total interest income − Total interest cost
= [Average interest yield on rate-sensitive assets × Volume of rate-sensitive assets

• Average interest yield on fixed (non-rate-sensitive) assets × Volume of fixed assets]
  − [Average interest cost on rate-sensitive liabilities × Volume of interest-sensitive liabilities
• Average interest cost on fixed (non-rate-sensitive) liabilities × Volume of fixed (non-rate-sensitive) liabilities]
  = 0.05 × $542 + 0.10 × [$1,212 − $542] − 0.04 × $156 − 0.06 × [$1,212 − $156]
  = $24.5 million

Note.
The balance sheet is based on the fundamental equation:
Assets = Liabilities + Equity

In this case, we've been told there's no equity, which means that:
Assets = Liabilities