This level is fairly simple. You can get 3 stars with 2 hits. Use 1 hit to take out the two pig at the lower elevation, and use the other to take out the two pig at the higher elevation. Killing two pigs with one shot may be somewhat of a challenge, so try a couple of times and you will get it eventually.
[youtube width=420 height=345 time=2]http://www.youtube.com/watch?v=0Yq0eleZmy0[/youtube]