To complete this level, you need to make your dart have a decently high power, and try to aim accurately for the Tack Bloons. If you aimed very accurately, the dart will be able to pop the Bomb Bloons.
Trivia
It is called "4 3 2 1 boom" because the dart bounces 5 times. In the first 4 times, it bounces to pop the tack bloons, while in the last time, it pops the bomb bloons.
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