I am still having some trouble with figuring out the net gain of C) 4.

The investor is forced to sell, but is it at $80 or the market price.

It would make more semse to me if it were at $80 because the investor looses and the buyer is the one that gains the market price - $80.

And if this is true then the investor's net gain is 80-78.54 = $1.46.