y =[x-8][ 100-(x- 10)* 10]
=(x-8)(200- 10x)=200x- 10x^2- 1600+80x
=- 10x^2+280x- 1600=- 10(x^2-28x)- 1600
=- 10(x- 14)^2+360
That is, when the price is 14 yuan, the maximum profit is: 360 yuan.