The staff reading at a distance of 80 m from a level with the bubble at its centre is 1.31 m. When the bubble is moved by 5 divisions out of the centre, the reading is 1.39 m. The angular value of the one division of the bubble, is

• 28.8 secs
• 41.25 secs
• 14.52 secs
• 25.05
• none of these