1, 500+300=800 points, the investor's profit reaches the maximum, and the buyer loses all royalties by 800 points.

2.15000-500-300 =14200 1500+300 = 15800. This is the profit price range.

The topic asks the trader, that is, the buyer, not the investor. 15900-15000-500 = 400 points; 400-300= 100, so the trader's income 100.

I hope I can help you. I think you just didn't see the topic clearly.

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