To find the initial height of the drone before it started rising, we need to first calculate a few things.
1. The rate at which the drone is rising can be calculated by dividing the rise distance by the time in which it was covered. Here, it's given that the drone rises 18 meters every 3 seconds. So, our rise rate becomes 18m/3s = 6 m/s. This means the drone rises at a rate of 6 meters per second.
2. We know that the drone was rising for 5 seconds. Therefore, we can find how high the drone actually rose during this time by multiplying the rise rate by the time. So, the height rise is 6 m/s * 5s = 30 meters. This means the drone rose 30 meters during the time it was rising.
3. It was stated that after 5 seconds, the drone reached 40 meters. This height includes its initial height before it started rising. We only calculated the extra height it gained during rise which is 30 meters. So to find the initial height, we need to deduct the extra height (height rise) from the total height it reached. So, our initial height becomes 40 meters - 30 meters = 10 meters.
In conclusion, the drone was originally at a height of 10 meters before Rebecca started making it rise.