Calculate the Object Distance from camera

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Ive read in this question that the object distance from the camera is

distance to object (mm) = focal length (mm) * real height of the object (mm) * image height (pixels)
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                          object height (pixels) * sensor height (mm)

I have a HTC M9s and a red ping pong ball.In this variables I only know the real height of the object (mm) and image height (pixels) and object height (pixels)

but I dont know focal length (mm) or sensor height (mm).how can I find them? How much is this reliable?