In this level, (as well as the blocks you need to match) you get two roto blasters, one line blaster and a bomb, plus the rocket (built up within the level) to destroy eight metal boxes.
In theory, all you need to destroy is two metal boxes with each booster, and you'll still have a spare booster for any stray blocks.
Try to keep the metal boxes aligned as much as possible and move a roto blaster, or the line blaster level with a row to destroy two or three at a time.
Don't destroy the infected block, as it's 'virus' can multiply over blocks that would otherwise not get matched.
Take your time and work your way down the board making efficient matches and destroying metal boxes carefully as you go.
Not all boards will be cooperative, so don't be afraid to quit and start again if things are not going well!