Blue Co$.$ purchased equipment on September $7,20$X$4$ for $$100,000.$ The equipment$$s estimated life is $4$ years and it has an estimated salvage value of $$3,000.$ The company uses double$-$declining$-$balance $($DDB$)$ depreciation and applies the half$-$year convention, which includes taking one$-$half year depreciation in the year of purchase and in the year of sale or disposal. Blue Co$.$ sold the equipment on July $10,20$X$6$ for $$30,000.$ What was the gain on sale?