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

$$3\mathrm{.}00$ a box. The lettuce is sold for $$15\mathrm{.}00$ a box and the dealer that sells old lettuce is willing to pay $$1\mathrm{.}50$ a box. Past history says that

tomorrow's demand for lettuce averages $250$ boxes with a standard deviation of $32$ boxes.

How many boxes of lettuce should the supermarket purchase tomorrow?

Note: Use Excel's NORM.S$.$INV$()$ function to find the $z$ value. Round your answer to the nearest whole number.