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the answer is -$97 for sure. TVBNOW 含有熱門話題，最新最快電視，軟體，遊戲，電影，動漫及日常生活及興趣交流等資訊。1 _$ U! J! B3 t" `" l' s" I: h
Think about it this way + G2 u; B6 o( N) X4 Z2 o  C& ?
1) if the 100 bucks is not a fake one, the store owner will gain $3 ($21-$18)tvb now,tvbnow,bttvb( L$ X4 i" F1 }8 |
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