please help, i keep getting the wrong answer.

The local supermarket buys lettuce each day to ensure really fresh produce. Each morning, any lettuce that is left from the previous day is sold to a dealer that resells it to formers who use it to feed their animals. This week, the supermarket can buy fresh lettuce for $9.00 o box. The lettuce is sold for $17.00 a box and the dealer that sells old lettuce is willing to pay $5.00 a box. Post history says that tomorrow's demand for lettuce averages 258 boxes with a standard deviation of 41 boxes. How many boxes of lettuce should the supermarket purchase tomorrow? (Use Excel's NORM.S.INVO) function to find the z value. Round your answer to the nearest whole number.) Number of boxes 260