Why is the depreciation expense listed as 2280 rather than the 4200 from the equation, and why is 1400 listed as a negative?

Year Depreciation Table for Equipment Depreciation pre annum= (30,550-1,150)/7 = 4,200 Value 1 2 N 3 4 5 30,550 29,150 26,870 24,590 22,310 Depreciation Accumulated Depreciation Balance 1,400 2,280 2,280 2,280 2,280 Accounting Equation Assets = Accounts Increase in Depreciation Expense Decrease in Vehicle Value 1,400 3,680 5,960 8,240 10,520 -1,400 29,150 26,870 24,590 22,310 20,030 Liabilities+ Equity -1,400