Safe Cracker (Bloons 2)

 is the 52nd level in Bloons 2, and the 4th level in the Rubber Jungle zone.

Solution
Get the dart through the Boomerang Bloon and let it hit the 4 normal bloons. Now get the boomerang to hit another Boomerang Bloon and contact the Bomb Bloon. The next step is by far the hardest part; aim the boomerang carefully so that it hits the Ice Bloons.