You cn only hit boxes on the bottom row.
If a box is destroyed, the boxes above it will fall down.
If the numbers on adjacent boxes form a sequence starting with one, all of the boxes in that sequence are destroyed.
Which boxes do you need to hit to destroy them all with just two cannonballs?
Touch a cannon to fire it at the correspoinding box.
Look for a box to destroy that will make the numbers line up.
First, aim at a box that occurs three times.
If you aim for a 2 first, lots of boxes will be destroyed, but it will cause you trouble later on.
There are two options for lining up a 2 with the 1 at the bottom-right.
Choose the one that gives you the longest number sequence.
Yhe first box to aim for is the 3 on the right.
Then look for the box that will make the top-left 1 join up with a 2.
The answer is as follows.
1. Shot to destroy the 3 on the far right.
2. Shot to destroy the 2 on the second from the left.