Answer
The answer is as follows. 
1. Put '2' on B-a.
2. Put '4' on C-d.
3. Put '5' on A-c.
4. Put '5' on C-c.
5. Put '3' on D-c.
6. Put '3' on B-e.
7. Put '2' on C-e.
8. Put '4' on B-f.
9. Put '4' on C-f.
Katrielle and the Millionaires' Conspiracy walkthrough
Puzzle Location: Foot of the Elizabeth Tower (Gudrun Weldon)
The bubbles on the left are the ones that have not been fired yet.
Touch a bubble and then slide it to move it.
If you drag a bubble onto the board and then stop touching it, it will be fired from the cannon onto the square where you placed it.
If there are not enough bubbles of a certain number, you need to add to them by firing bubbles from the cannon.
There are several ways to do this, but let's take one example.
First, pop the '4' bubbles in the centre.
Be sure not to pop the '4' at the top-right.
Continuing on from hint two...
The next bubbles to pop are the ones with '5' on them.
You need to fire more '5' bubbles from the cannon to get them up to the right amount.
Countinuing on from hint three...
Now you need to pop the '3' bubbles.
First, fire a '3' into the gap at the bottom to burst the '3' bubbles at the bottom and left.
If you don't tackle the '3' bubbles correctly here, you will run out of bubbles to fire from the cannon.
The answer is as follows.
1. Put '2' on B-a.
2. Put '4' on C-d.
3. Put '5' on A-c.
4. Put '5' on C-c.
5. Put '3' on D-c.
6. Put '3' on B-e.
7. Put '2' on C-e.
8. Put '4' on B-f.
9. Put '4' on C-f.