$A$ distant hot air balloon subtends $0.25^o$ at the objective lens of an astronomical telescope. The image subtends $1.5^o$ at the eyepiece when viewed with a relaxed eye. The objective and eyepiece are in a $35 \ cm$ long tube. Find the focal length of the eyepiece lens in $cm$.

  • A
    $10$
  • B
    $3$
  • C
    $5$
  • D
    $7$

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