Answer:
$8.75
Step-by-step explanation:
Let x = the amount the man originally had
The man has $x and says "if you give me $x, I will spend $10."
y = amount he has after 1st proposition = x + x - 10 = 2x - 10
He repeats this procedure, now with $2x-10 in his pocket...
z = amount he has after 2nd proposition = (2x - 10) + (2x - 10) - 10 = 4x - 30
He repeats this procedure, now with $4x-30 in his pocket...but this time he is left with zero dollars...
r = amount he has after 3rd proposition = (4x-30) + (4x-30) - 10 = 8x-70 = 0
8x - 70 = 0,
x = $8.75