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7. What are the two figures to replace the question marks?
  12 17 15 20 18 ? ?
 

Explanation:
Numerical sequence: + 5, - 2, + 5, - 2, ... (12 + 5 = 17; 17 - 2 = 15; ... 18 + 5 = 23; 23 - 2 = 21).