Your post gives no commission rule after 30 units so im not sure how we are supposed to comment on the commission for 600 units.
From the information, exactly as you posted it, i get:
number of units = x
commission = 150*min(x,10) + 200*min(max(x-10,0),10) + 250*min(max(x-20,0),10)
The above formula assumes that no commission is paid after the 30th unit (which is where you stopped your post). Test before use.
Your rule and the above formula gives
Commission for 600 units = Commission for 30 Units = 6000