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The number of "-9" is 12 units away from the number of "3", so there are exactly TWO PERIODS distance between them.
Therefore, f(-9) = f(3) = -1. ANSWER
The number of "20" is 12 units away from the number of "8", so there are exactly TWO PERIODS distance between them.
Therefore, f(20) = f(8) = 5. ANSWER
All questions answered. The problem is fully solved and completed.