I want to ask how to get 1.645,why not 1.96?

An analyst has been asked to estimate the VaR of an investment in Big Pharma Inc. The company's stock is trading at USD 23, and the stock has a daily volatility of 1.5%. Using the delta-normal method, the VaR at the 95% confidence level of a long position in an at-the-money put on this stock with a delta of -0.5 over a 1-day holding period is closest to which of the following choices? USD 0.28 USD 0.40 USD 0.57 USD 2.84