Deductions & credits

Thanks for the info.  We didn't take a previous tax deduction for any casualty loss.  For example, we had roof damage of $20 K and the insurance company paid us $15 K (after the deductible).  Using this scenario, I would enter $20 K on line 3a, $ 15 K on 3b and "0" on 3c since the values are net and we didn't take a deduction previously on any tax return.  Thus we have a $5 K increase in basis.  Thanks