﹙40≤x≤60﹚

2.y=- 10x？ + 1 100x-28000=- 10﹙x-55﹚？ +2250

So when x=55, y is the largest. That is, the maximum profit per day is 2250 yuan.

3.y=- 10x？ + 1 100x-28000=- 10﹙x-55﹚？ +2250=2240

x-55= 1，

x=56，54。

Selling this walnut in a specialty store wants to earn an average of 2240 yuan a day. In order to benefit customers and win the market as much as possible, it should be sold in 56 yuan and 54 yuan.