I completedall 30 and it says I need 21 more. This is because I had already completed 21 levels before the challenge existed. Someone needs to fix this, because I'm seriously pissed about it.
Try just blowing up all the mines you can with the shield whenever you have one. Each one gets as many points as a bubble, without having to be cautious.
Once I was pretty sure I got the badge, I just commited suicide by taking only the handgun and grenades at level 18. Very boring after you get the Mini-gun.
Is it just me, or did the higher levels cause everything but the ball to move slower? The paddle lagged, the "bricks" lagged, but the most important ball kept right on flying.