This is a simple arc that goes up and to the right, popping the nearest Pac-man bloon.
There are also frozen bloons at the bottom. For the first shot, select a steeper angle and a higher power, so that you pop the leftmost 3 mine bloons, the dart goes off the top of the screen, and it comes down and pops the rightmost 3 or even 4 mine bloons.
This should leave you with a score of 45, two more than the target 43. You want a pretty strong shot that goes high and slightly to the right strong enough that it goes briefly off the top of the screen , and then comes down and pops both of the "outside" tack bloons.
This should be a medium-power, medium-arc shot that goes through the row of 6 normal bloons that lies between the row of mine bloons and the row of ice bloons, WITHOUT hitting any mine bloons or ice bloons. You have to get the missle in between the bloons, but it is a tight pi … nch. Even with my vast Bloons experience, it took me 15 minutes of playing to beat the level again while writing this.
Note that it is possible for the bloon to enter the upper side of the bloon mass, and enter out the right side, without popping the tack bloon. Aim a strong shot directly at the remaining tack bloon.
Even with all my experience, it's hard to get all three darts into the vault. You have to move right one and a half spaces, centering your Pac-man over the two rightmost columns of bloons. Pop one of the breakable walls. This will take your score up to 55 or so, or as much as 60. Would you like to merge this question into it?
But if you manage to clear the top and bottom rows, and one column, you'll have gotten a score of 66 or 67 or so. You only have one dart with which to pop 22 out of 27 bloons. Still, this method can. And then you can use the normal shot to "clean up" the best bunch of remaining bloons. On the other hand, a low arc shot can also enter the gap, but the margin of error here is much smaller, and you'll usually hit the wall on either side.
You can probably shoot almost any way you want here, and still set off the chain reaction that totally clears the playfield objects. This is a little tricky, but you just have to do an arc to get the dart in the gap between the walls above the uppermost tack bloon.
Generally, a max-power shot is better on the bottom bloons, and you can usually pop all but one or two of the bloons.
The multi-dart bloon in the lower-right will probably still be there, and since this will be your last shot unless you pop that multi-dart bloon, you'll have to plan accordingly. These will be max-power, straight shots angled up and to the right, "peeling" off diagonal columns of bloons from left to right. The innermost 2 or 3 bloons on each side seem to be impossible to reach this way, so you must use the aforementioned bounce-off-the-rubber-walls shots to pop them.
Second shot if needed: