Ghostface killa said
Toy can't discount the initial investment
Add a couple zeros and now you're talking about paying back investors.
The very first number you discuss is the ROI
This is a business conversation and it needs to be approached as such.

No. It's simple math, and simple math is the basis of business.
There were two business dealings with 2 transactions each.
First he invested $800, then was paid $1900.
He profited $1100.
Secondly, he invested $1100, then was paid $700
His loss was $400.
That's all that happened.
But the first investment was his startup so it put him in the negative. The second investment was profit so it left him in the positive.
He's left with his initial startup for the first purchase which puts him at $0 and the remainder of the profit of the initial sale which leaves him at $700 profit.
Any other answer is wrong.