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 $3.00 a box. The lettuce is sold for $14.00 a box and the dealer that sells old lettuce is willing to pay $1.50 a box. Past history says that tomorrow's demand for lettuce averages 235 boxes with a standard deviation of 35 boxes. How many boxes of lettuce should the supermarket purchase tomorrow? (Use Excel's NORM.S.INV() function to find the z value. Round your answer to the nearest whole number.) Number of boxes