Look at the 2nd image, which is level 21. The solution: the bottom right 4 shoots to the left. That allows the bottom 3 to move up. Because it travels in front of that middle 4, that middle 4's path gets extended just enough to cross the 4 at the top. The 4 at the top comes down, just in the path of the 2, which can then reach the white square.
There are 100 levels and I aim to do them all. At the moment I'm stuck on level 36.
Zhed is fun and free. Download it now.