I would say $20. It seems like he loses 10 bucks by buying it back at a higher price, but that assumes he only had that starting capital ($60) to begin with. Since he buys back at a higher price it's clear he had more investment capital than just that $60, so he makes $10 bucks each trade through two different trades.
Licorice
When you smell like sour patch straws lets a thug nowLicorice
Exactly what this man said. It's two seperate deals but it's intentionally read as one continuing deal to try to make you lose count.
Following the money trail, he made $10 overall.
Buy for $60, sold for $70 = $10 profit
Take $70 and add another $10 and buy back the item for $80 = $80 in the hole
Sell the item for $90 = $10 profit from all transactions.