Here's how to solve the problem: * **Understanding the terms:** * RL (Reduced Level): The height of a point above a datum (reference level, often mean sea level). * Backsight (BS): A reading taken on a point of known elevation (benchmark). * Inverse Staff Reading: A reading taken with the staff held upside down, typically on a roof or overhead feature. * **Calculation Steps:** 1. **Height of Instrument (HI):** The height of the level instrument above the datum. * HI = RL of Benchmark + Backsight * HI = 100.00 m + 3.25 m = 103.25 m 2. **RL of Roof Station:** When using an inverse staff, the reading *adds* to the HI to get the roof's RL. * RL of Roof Station = HI + Inverse Staff Reading * RL of Roof Station = 103.25 m + 1.25 m = 104.50 m Therefore, the RL of the roof station is 104.50 m. This falls within the requested range of 104 to 105. **Final Answer: 104.50**

Here's how to solve this problem: * **Understanding the Concepts** * **Backsight (BS):** A reading taken on a point of known elevation (in this case, the benchmark). * **Reduced Level (RL):** The elevation of a point above a datum (reference point). * **Inverse Staff Reading:** When measuring upwards from an instrument, the staff is held upside down. This is common in tunnels or under bridges. * **Calculations** 1. **Height of Instrument (HI):** This is the elevation of the line of sight of the leveling instrument. HI = RL of Benchmark + BS HI = 100.00 m + 3.25 m = 103.25 m 2. **RL of Roof Station:** Since the staff is held upside down, the reading needs to be added to the HI. RL of Roof Station = HI + Inverse Staff Reading RL of Roof Station = 103.25 m + 1.25 m = 104.50 m * **Answer** The RL of the roof station is 104.50 m. This value fits between 104 and 105, as requested.