To estimate the number of drones needed for FedEx deliveries in the US, we need to make several assumptions. First, let's assume we're delivering all packages ordered within a single day to residential doorsteps. We also need to consider the total number of packages FedEx handles daily in the US. This requires estimating the percentage of the US population (approximately 330 million) that orders goods online, factoring in demographics like age and internet access. Then, we'd need to determine the average number of online orders per person per year and divide that by the number of delivery days in a year to get daily orders. We also need to consider the capacity of each drone (package size, weight, and delivery range) and the time it takes for a drone to complete a delivery cycle (pickup, travel, drop-off, return). Finally, by dividing the total daily package volume by the number of packages a single drone can deliver per day, we can estimate the total number of drones required.