The additional 180 - 160 = 20 bicycles cost an additional $11,000 - 10,100 = $900. That means the 180 bicycles cost 9·$900 = $8100, and the fixed costs are $11,000 - 8,100 = $2,900.
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Each group of 20 bikes costs $900, so 9 groups of 20 (180 bikes) cost 9×$900 = $8100.