10x+200y=90000

12x+ 120y=90000

Solution: x=6000, y= 150.

(2)

Set up a computer and B desk.

6000 * 0.9a+ 150 * 0.8b = 270000

a≥35

a=35，b=675

a=36，b=630

A=37, b=585 (obsolete)

So there are only the above two schemes.