How can I calculate that? Is there any formula for this calculation or what should i do?

Question 30 0 out of 0.5 points Flukey Gold Mines makes an unexpected announcement regarding gold production at 2.20 p.m. Shares of the company were traded at 12 p.m., 2.10 p.m., X 2.30 p.m. and 4 p.m. If the market for Flukey Gold Mines' shares is efficient, then at which trade will the newly established share price fully reflect the new information? Selected Answer: @ 2.10 p.m. Answers: 12 p.m. 2.10 p.m. on the opening of the next trading day 4 p.m. 2.30 p.m. Response Feedback: incorrect