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the answer is -$97 for sure. tvb now,tvbnow,bttvb! s: ?: X; Q: r" }7 u. Z
Think about it this way
# S& G) W5 r/ R3 u! V' r1) if the 100 bucks is not a fake one, the store owner will gain $3 ($21-$18)TVBNOW 含有熱門話題，最新最快電視，軟體，遊戲，電影，動漫及日常生活及興趣交流等資訊。0 M/ U2 B$ r( H
2) Now, the owner discovered that the 100 bucks is fake. You can think this as a lost of $100. therefore the overall gain is $3-$100 = -$97