So profit is the profit of each commodity * sales volume: [500- 10*(x-50)]*(x-40),
Simplify to (500- 10x+500)*(x-40), continue to (1000- 10x)*(x-40), and finally get.
10( 100-x)(x-40), that is to say, find the maximum x value of this formula.
-10[(x-70) squared -900], so x=70 and the profit is 9000.
answer