First, we need to know how much Bert paid for the barrel in the warehouse, and that is 90 - 10 = $<<90-10=80>>80.
The tax from the sale stands at 10/100 * 90 = $<<10/100*90=9>>9.
That means Bert earned 90 - 9 - 80 = $<<90-9-80=1>>1 on the sale.
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