Final answer:
The elevation of the inner hachured line at the top of Mt. Hall can be determined by counting the number of contour lines and multiplying it by the contour interval.
Step-by-step explanation:
The elevation of the inner hachured line at the top of Mt. Hall can be determined by looking at the contour lines on the map. The contour interval is given as 20 ft, which means that each contour line represents a change in elevation of 20 ft. Start counting from the inner hachured line towards the top of Mt. Hall, and multiply the number of contour lines by the contour interval (20 ft) to determine the elevation.
For example, if there are 5 contour lines between the inner hachured line and the top of Mt. Hall, the elevation would be 5 x 20 ft = 100 ft.