Answer: a. Increase liabilities and decrease stockholders' equity.
Step-by-step explanation:
Contingent Liabilities are obligations that the company may owe if a future event happens such as them being ruled against in a case in court.
Contingent Liabilities are to be recorded in the financial statements only when it is probable that it will happen and that the amount to be paid is reasonably estimable.
Company A's management feels like the loss is probable and that they would have to pay the full amount to company B which means that the loss is both likely and estimable.
Company A should therefore increase their liabilities and debit loss which will come from the Equity thereby reducing it.