A 2500 m long line lying at an elevation of 400 m measures 12 cm on a vertical photograph. The focal length of the camera is 20 cm. The scale of the photograph for an area having an elevation of 1000 m will be ?
1
1 ∶ 17980
2
1 ∶ 17833
3
1 ∶ 18456
4
1 ∶ 17865