Since the rate of depreciation is constant, the amount of depreciation decreases by $200 each year. The depreciation in the first year is $7000 and in the second year is $6800, so the amount of depreciation in the third year is $6600. Following this pattern, the depreciation in the fourth year would be $6600 - $200 = $6400. The depreciation in the fifth year would be $6400 - $200 = $6200. Therefore, the amount of depreciation in the sixth year would be $6200 - $200 = $6000.
Therefore, the answer is option 2. $6000.