This level is mostly easy. However, be careful of Prospector Zombies, as they have Dynamite attached to their hips that will detonate and launch them to the first column. After that, they will start eating the player's plants from behind.
Don't plant the Twin Sunflowers in the first column. Plant it in the second one, so when Prospector Zombie comes, defeat them with Spikeweeds.
Now, plan your attack and defense. Since Snapdragon's range is limited to a 3x2 area, you should plant it near the zombies. Plant Bloomerangs on the minecarts. Plant Wall-nuts to protect the Snapdragons and the Bloomerangs.