Simplify the following text for a Grade 6 native English-speaking person.
Original: The Gunnedah Colliery Company was registered in May 1899 and by 22 June a private railway some 5.7 k in length had been completed from the railway station to their mine .
Simplified: The Gunnedah Colliery Company was registered in May , 1899 . One month later a private railway some 5.7 km in length had been completed from the railway station to their mine .