The answer has to be 1$.
If he bought for 5$ and sold for 7$. you have a extra 2$ in your pocket.
The next transaction you buy for 9$, it cost you that 2$ profit plus an additional 2$. You then sell for 12$, after you pay yourself back the 2$ you lost on the 2nd buyback, you have 1$ profit.
i failed calculus 2x in college because i hated math so much. on the other hand, i aced statistics and enjoyed the hell out of it. my natural strength is creative writing and communications.
i'm diggin that a banker used the same logic as me and came up with +1. what's the proposed answer and logic Extraordinary?