Both parties put $20 in, losing $20 each

Person B pays $30 for the box, making his current profit -$50

Person A receives the $30, making his profit +$10

Person B gets the box with $40 inside.

50 - 40 = 10

Person B just got scammed out of $10.

Thus giving person a infinite money

my mind didn’t comprehend that I need an explanation

oh wait nvm I get it

I'm trying to calculate if this would work or not

I calculated it i think