Extracted text: 20. A trapezoidal open channel has a bottom width of 1.34m and its sides slope is 45•00'. The constant height of water is 2. 20m. determine the cross sectional area of the stream up to that level. a) 9.455sqm b) 8.456sqm c) 7.755sqm 21. The elevation above sea level of two end poits of a base line for a triangulation system, as determined by differential leveling, are: 2,683.45m and 2,615.22m. Determine the mean sea level length of the line if the actual measured horizontal length is 5,525.850m. Assume the radius of the earth at the vicinity of the base line is 6, 423.349 km. a) 5523. 571m b) 5513.454m c) 5509.678m 22. An object was observed from a triangulation station. The measured distance was recorded to 4985.78m. determine the combined effect of earth's curvature and atmospheric refraction. a) 2.123m b. 1.789m c) 1.665m 23. From a topographic survey, the elevations point A and B were determined to be 233.7m and 247.7m. Contour line are to be drawn that will cross the line AB. If the contour interval is 2m, determine the how many contours that could be drawn along line AB. a)9 b) 5 c) 7