where is young man's $29 gain in your calculation? plus
I am afraid this is not a -50 sum game.
To zero sum analysis,
1)no fake money
young man:
money: -$15
good: +$15
sum:0
owner:
good: -$15
money:+$15
sum:0
total=0
2)with fake money
young man:
money: +$29
good: +$15
sum: +$44
neighbor: $0
to make the total zero, owner must be -$44