Shadrach Heating and Air Conditioning, Inc., borrowed $15,000 from the Meshach Merchants Financing Association (MMFA) in order to purchase a new furnace for its own home office. When one of its important clients needed an identical furnace in a hurry, Shadrach Heating sold it its own new furnace, which it installed in the client's place of business. The $17,000 check it received in payment was put into Shadrach's checking account (balance prior to this deposit: $81) with the Abednego State Bank. Thereafter, Shadrach made one further deposit of $5,000, followed a week later by a withdrawal of $5,040. If Shadrach Heating defaults on its loan repayment to MMFA and also on an unsecured promissory note currently held by the Abednego State Bank, can the bank exercise its common law right of setoff and pay itself out of the checking account, or is its setoff right junior to MMFA's security interest in the proceeds