One expiry before, one after

A Union Budget falls between two weekly expiries. The expiry before it (2 days) trades at 11% IV, the one after it (9 days) at 16%. Ordinary volatility between them is estimated at 12%. (a) Prove (9A.14). (b) Compute the event variance, its standard deviation and expected absolute move, in percent and in points with the index at 24,500. (c) How does the answer change if ordinary volatility is 14% instead of 12%? What does this say about the precision of event extraction?