Answer:
9
Explanation:
2 + 1 + 4 + 3 + 5 + 7 + 4 + 2 + 2 + 1 + x = 40
x = 40 - (2 + 1 + 4 + 3 + 5 + 7 + 4 + 2 + 2 + 1)
x = 40 - (3 + 7 + 12 + 6 + 3)
x = 40 - (10 + 18 + 3)
x = 40 - 31
x = 9
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