Riddle: A young man decides to buy a collector's baseball card. He pays $60 for it. After a month, the value of the card has increased to $70 and he decides to sell it. But already a few days later he regrets his decision to sell the collector's item, and he buys it again. Unfortunately he has to pay $80 to get it back, so he loses $10. After a year of owning the baseball card, he finally decides to sell it for $100. What is his overall profit?