You bought two antique lamps for $50 each. Later, you were offered $60 for one and sold it, change your mind when you saw its duplicate being sold for more and bought it back for $70. You then sold it for $80. The first one didn't sell at all so you reduced it 10% below what you originally paid and managed to get rid of it. Did you make money or lose money on the deal and how much?
You made $15. Simply add up all the money laid out and all the money brought in. The fact that you bought the same lamp twice is irrelevant.
