Crossword puzzle

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Across
  1. 4. how many keys does a piano have?
  2. 5. to understand fully
  3. 7. synonym of feasible
  4. 8. something that happened recently
  5. 9. to make something difficult
Down
  1. 1. something possible/easy to achieve
  2. 2. vest K-pop boy group
  3. 3. to grow, develop or be successful
  4. 6. Batman’s son