Answer: Strong form.
Explanation:
The Strong form efficient market is one where all the information regarding a stock is are already reflected in the stock's price. All information means that both private and public information are accounted for.
The plan to offer $75 per share for the small competitor was decided in a private board meeting yet as soon as the meeting was over, the proposed price had already reflected in the OTC market price. This shows that the market is strong form efficient.