A theodolite has a multiplying constant of 100 and when set up at position A has a height of 1.20m. When sighted onto a vertically held levelling staff at position B, the horizontal centre line gives a reading of 1.40m and the upper and lower stadia lines read 2.00m and 0.80m respectivelly. If the angle of elevation of the instrument is 6°20'. , calculate the horizontal distance?