There is no difficulty in this level at all as you can use any plants and the zombies are extremely weak.
Conehead Mummy x1
Health: 3888 Fighting Power: 360 First Strike: -- Features: Lower general attack and defense Skill: The zombie uses its bandage whirlwind to attack, posing a threat to enemies in front of it. Leader Skill: [Primary militant high]
Flag Mummy Zombie x2
Health: 3240 Fighting Power: 360 First Strike: -- Features: Skill: Waves a flag, encourages zombies, heals the three lowest health by percentage in the zombies' team. Leader Skill: [Primary militant high]
Follow the tutorial, drag the plants you need into the lawn and you should win.