I was not given the value for depreciation, I have been given the accumulated depreciation for the two years. I took the difference and got a value for depreciation which I used in calculating the net book value and also added to profit before tax.
But the solution did something different.
It took the difference between the accum. Depreciation for the two years and still added the depreciation on an asset disposed that year.
When an asset is disposed of then accumulated depreciation on the asset sold is removed from the balance brought forward on the accumulated depreciation account.
Therefore the depreciation expense for the year is the difference between the closing balance on the accumulated depreciation account and (the opening balance less the depreciation on the asset sold).