## 2 Literature Review  
The literature review focused on mathematical models that considered unmanned aerial systems, in this case, combined with the traditional delivery approach. It can be seen that the most common are the Vehicle Routing Problem (VRP) and Travelling Salesman Problem (TSP) for Unmanned Aerial Systems. The authors emphasize that the classic VRP configurations according to the characteristics of the UAVs are functional with this mode of transport; it should be noted that this mathematical model focuses only on the use of UAVs, therefore, it is very different from the mixed model that is proposed in this investigation. [PERSON] et al. [23] presented a VRP, objective to minimize the maximum 130 duration of routes. The variant of the VRP that they used was the delivery and collection (VRPD); they consider that the use of drones and trucks would be a common practice, therefore, companies from the United States and Europe consider this alternative. The study presents various theorems where each one contemplates the savings that organizations can obtain by implementing this technology. [PERSON] et al. [24] presented a VRP model based on the VRPD variant. The objective of this study was to expand and strengthen the previous results in its article emphasizing the importance of drones in industries such as Amazon, Google, DHL, and Walmart. They demonstrate the maximum benefit of the model presented in ideal circumstances, taking into account a series of UAVs with a speed greater than that of a truck, presenting important practical advantages. The authors claim that the UAV returns to the top to recharge the battery quickly; its main objective is to minimize delivery times in the last mile. [PERSON] and [PERSON] [25] used the Vehicle Routing Problem (VRP) with windows of time contemplating the delivery of packages between drones and trucks, concluding that this new modality gives competitive advantages to companies, and the benefit of the use of UAV is relevant. These time window restrictions are useful for the mathematical formulation that is proposed in this study; the important thing is the consideration of time windows for customer service and other jobs do not add them and propose an exact model. [PERSON] et al. [26] have a new way to further exploit this technology in delivery systems. They propose that drones can supply delivery trucks in the last mile using a VRP and algorithms found the advantages of saving costs and travel faster than vehicles since they are not limited the road network and traffic congestion. The work by [PERSON] and [PERSON] [27] is the first study that introduces TSP-D, the Flying Sidekick Traveling Salesman Problem (FSTSP) which provides one solution by allowing delivery trucks to deploy UAVs. It is based on a route first-cluster; they improved delivery times using drones in the truck route using a heuristic for their solution. Delivery times improved as trucks were included and drones were integrated to improve deliveries, but they did not contemplate the time windows. [PERSON] [28] used simulated solutions for the model, where the results were favorable for the FSTSP since he considered that it may be more practical in the real world because the use of drones allows a considerable amount of time to travel through a set of nodes. This is viable to improve and optimize the delivery of packages. [PERSON] and others [29] used the TSP model; in comparison to other articles mentioned, they proposed an optimization algorithm to determine the optimum number of launch sites and locations that have delivery requirements with drones and trucks. They reduced delivery times and determined that this technology outperforms trucks in energy efficiencies when they are delivered to one hundred customers in a delivery distance of 100 km.