You are tasked with deploying a web application to Google App Engine, and it’s crucial that the application responds efficiently to varying levels of user traffic. To ensure optimal performance, you need the number of instances to dynamically adjust based on the request rate. Additionally, it is a requirement to always maintain a minimum of 3 unoccupied (idle) instances available to handle incoming requests promptly. Given these requirements, which scaling type should you configure for your App Engine deployment?