Final answer:
To prevent administrators from creating virtual networks in RG-RG, implement an Azure RBAC policy to restrict permissions, or set an Azure Policy to deny the creation of virtual network resources in that specific resource group.
Step-by-step explanation:
To ensure no other administrators can create virtual networks in the resource group RG-RG at Radio Gaga, LTD, you can implement an Azure Role-Based Access Control (RBAC) policy. By assigning a custom role to administrators or modifying an existing role, you can set the permissions so that they exclude the ability to create virtual networks within RG-RG. Additionally, you can use an Azure Policy to enforce rules that prevent the creation of virtual networks within that specific resource group. This policy can be set to deny the creation of all virtual network resources, which would effectively prevent any administrator from provisioning new virtual networks in RG-RG.