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.