✔ 最佳答案
Does any part of your question related to calculation of tax???
Usually, written-down value is talking about the tax allowance (i.e. depreciation allowance) for tax calculation. However, if your question doesn't have any part related to tax, I think the written down value may be talked about the NBV (net book value). It is used for the calculation of gain on disposal of machinery.
In your question, the gain on disposal of machinery is $12800 ($30000-$17200). This amount should be adjusted (i.e. deduct) in cash flow statement as it is not related to the actual cash inflow/outflow. It is just a part of P/L item. The actual cash inflow is $30,000.