On 30 just cut one of the columns straight down to about the red line, then whiz your cursor over to the bottom of the other column as it falls and it you'll take it out in time to catch the 3 leftover in the original column before they topple the towers. I think I did it 14 times in a row. Sweet level planning!
I love this game. It is so addictive. But I will never play again now that I did it in four. Please don't make any more games. I have a job and a family.
A good concept, and i like games that have a bit of randomness even within one "level", but there is no way to come up with a good strategy if the enemies change too much from one attempt to the next. Unbalanced.