Then the profit of each shirt is (x-40) yuan and the sales volume is [500- 10(x-50)].

According to the meaning of the question, list the equation [500-10 (x-50)] (x-40) = 8000.

Arrange to x2- 140x+4800=0,

X 1=60, x2 = 80 is used to solve the equation.

Because when the price is high, the quantity of imported goods is small and the cost is small.

Therefore, in order to use the least cost, merchants still make a profit of 8,000 yuan, and the price should be set as 80 yuan.

A: The price should be set at 60 yuan or 80 yuan. In order to make a profit at the minimum cost, the merchant still paid 8000 yuan, and the price should be set as 80 yuan.

2. Suppose the price of each commodity should be set at X yuan, and P pieces of this commodity should be sold every day.

According to the meaning of the question: (x-30)( 100-2x)=200,

Finishing: x2-80x+ 1600=0,

∴(x-40)2=0，

∴x=40

∴p= 100-2x=20 (pieces);

Therefore, the price of each commodity should be set as 40 yuan, and 20 such commodities should be sold every day. I don't know what the third question means.