$\begin{array}{c|c} & N \\ \hline sales & 45,000 \\ \text{Opening stock} & 20,000 \\ \text{Closing sock} & 30,000 \\ Expenses & 15,000 \\ \text{Fixed assets} & 40,000 \\ Debtors & 10,000 \\ Creditors & 5,000 \\ Purchases & 25,000 \end{array}$

The cost of goods sold is

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