i took a different approach on my level 39 and had all combo towers with slow towers mixed in...if i could have purchased 4 extra lives it would have been beaten and i made some mistakes while working on this level....if i had sold some of my combo towers right before i was about to lose lives and bought the extra 4 lives or 8 just to be safe it would have cost me 320 and then my other 8 towers could have finished the last few off the second time around...level 39 is possible to beat