maths (completing the square)

If Good X has production cost of $2,

as it sell at $5, the quntity sold is 200,

if the price decrease for each $0.1, quantity sold will increase 10

a) find the selling price of Good X which get the maximum profit;

b) find the maximum total profit per dayin selling Good X

show steps , thx!!!

更新:

Re 自由自在:

you are so fast

that I even can't choose you as the best because the system do not allow

Thx a lot

還有問題嗎?立即提問即可得到解答。