( 1)

Functional relationship between y and x: y=300+20x.

(2)

Selling this commodity for 6000 yuan a day is not the biggest profit, for the following reasons:

You can find the functional relationship between w and x:

W=y(60-x-40)

=(300+20x)(60 x 40)

=(300+20 times) (20 times)

=-20x？ + 100x+6000

=-20(x-5/2)？ +6 125

Where 0≤x≤20

∴ When x=5/2, w has a maximum value of 6 125.

∵q 6000 & lt； 6 125, ∴Q6000 is not the maximum profit.

At this time, the price of the commodity should be: 60-2.5=57.5 (yuan).