Stuck on plants vs zombies wild west day 12

I'm on stuck on day 12 on plants vs zombies Wild West.
It's on the iPhone and nobody not even YouTube seem to have the walkthrough. It's the one where it's says "survive zombie attacks" and they start you off with the boomerang. Throughout the entire game it's just the boomerang and the lighting reed. I keep dying during the last wave can't seem to get through the bucket heads! Been stuck for 5 days now.

- Use the "View" option below the "Pause" icon to view the zombies.
- Adjust the formation then deploy the new plant, repeat.
- Boomerang: Plant them on mine carts only!
- Lightning Reed: Place them on land only (1st 3 columns), not on mine carts!
- Focus at least 3 attackers on Buckethead zombies then move to the lesser ones.