This is easier if you have completed or have almost completed the main game. You can use the Easy difficulty setting. You will then have the advantage of upgraded perks (Armor, Regen, Speed and Ramming recommended) and money. You cannot use your main cannon or machine gun. However, you can use Bunker Buster bombs (red bomb at the "Support Slots" screen). You will need at least four of them, at a cost of $1,000 each. Choose the first mission, "Village" at the mission selection screen. This mission requires you to blow up four buildings then leave, allowing for quick completion. Do not do anything else except destroying the buildings. Running things over is fine, as your upgraded perks will prevent damage. When your tank gets close to a mission building, use the Bunker Buster to destroy it.