Hey there!
12 - 7 - 8 - 9 + 66 = ?
12 - 7 = 5
5 - 7 - 8 - 9 + 66
5 - 8 = -3
-3 - 9 + 66
-3 - 9 = -12
-12 + 66 = 54
Answer: 54
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