Imagine a drone flying high up in the sky. This drone needs to land on a long runway strip on the ground. However, it cannot just fly straight down from its current height, as it may crash or have a rough landing. For a safe and smooth landing, the drone needs to be at a specific lower height when it reaches the start of the runway. It's like a plane approaching an airport - it has to descend gradually to the correct altitude before touching down on the runway. The question we need to figure out is: At what point should the drone start descending from its current high altitude, so that it can come down to the required lower height just as it arrives at the beginning of the runway? Getting the timing and distance right for when the drone starts its descent is crucial for it to land properly and safely on the runway. We don't need to worry about the exact numbers for now - the key is understanding that the drone has to plan its descent carefully to hit the right altitude at the right time and place.