The trick to passing this Level is in lining up the metal boxes so they can be removed with only a few line blasters.
Let the virus blocks multiply as they are a great way to remove large groups of blocks in one move.
Concentrate on getting the metal boxes in a row where they can be destroyed by the line blasters within the board and the one you'll build up as you play.
After most of the blocks are gone, then work on bringing the Pets down.
If you've left the virus to multiply, then by now it should be a large easier group to remove