(1) Assuming that the sales price should be X yuan, the unit profit is (x-50). Because every dollar increase will reduce 20 pieces, it is said on the basis of pricing 60 yuan, so the number of pieces reduced is (x-60)×20=20x- 1200.
So the sales volume is 800-(20x-1200) = 800-20x+1200 = 2000-20x, so the profit is 12000 yuan, and the equation (x-50) (2000-20x) = It's similar to the last question. You can simplify it and ask again.
The last question is the same. You should be able to do it in this way.