A taxpayer's gains and losses pertaining to business assets for the year are as follows: Gain due to insurance reimbursement for vehicle theft: $20,000 Loss due to insurance reimbursement for fire damage to a building: $(7,000) Gain due to building condemnation: $2,000 Loss on sale of investment property: $(18,000) There are no non-recaptured net section 1231 losses from previous years. What is the tax treatment for the casualty and theft transactions?

The answer is Net section 1231 gain of $13,000 but I am not sure why?