(40-30+x)(600- 10x)= 10000

- 10x？ +500x-4000=0

x？ -50x+400=0

X=40 or x= 10.

A: The price of each lamp is 10 yuan or 40 yuan.

When x= 10, the purchase quantity is: (600-10x) = (600-10/0) = 500.

When x=40, the purchase quantity is: (600-10x) = (600-10.40) = 200.