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 farmers who use it to feed their animals. This week the supermarket can buy fresh lettuce for $12.00 a box. The lettuce is sold for $25.00 a box and the dealer that sells old lettuce is willing to pay $3.50 a box. Past history says that tomorrow's demand for lettuce averages 280 boxes with a standard deviation of 46 boxes. How many boxes of lettuce should the supermarket purchase tomorrow? (Use Excel's NORMSINV() function to find the Z-score. Round intermediate calculations to four decimal places. Round your answer to the nearest whole number.)