As the guy above said, there are 4184 Megajoules in a ton of TNT. You just need to do some basic dividing
289351852 Megajoules / 4184 Megajoules = 69,156.75 Tons of TNT or 69 Kilotons
Looking at the
Attack Potency page, this is
Town level+
If you want a simpler way to find Tons of TNT, i recommend using
this energy converter. Note that it will not insert values with commas ( , ) so you have to remove them for it to accept the number and convert it