It is the first answer, loss of $701.80
The answer is 106 your welcome :-)
The coordinate (5,-6) lies in the fourth coordinate, because the first is x positive y positive, the second is x negative and y positive, the third is x negative and y negative, and the fourth is x positive y negative. This is x positive y negative, so it is in the fourth quadrant.
If
then the derivative is
Critical points occur where 
. This happens for
In the first case, we find
In the second,
So all the critical points occur at multiples of 
, or 
. (This includes all the even multiples of .)
