On June 1 2008, China implemented the "Plastic Restriction Order" and began to use reusable shopping bags for compensation. In order to meet the market demand, a manufacturer produces two models, A and B. Solution: (1) According to the meaning of the question:

(2) According to the meaning of the question:

Solution element

∴y decreases with the increase of X.

When x=3500,

A: The highest daily profit of this factory 1550 yuan.