Which AWS service or tool will meet these requirements?

Explanations:

AWS Auto Scaling automatically adjusts the number of EC2 instances in response to traffic demand, ensuring the application can handle increases in load while optimizing costs by scaling down during low demand periods.

AWS Compute Optimizer helps recommend optimal AWS resources for your workloads, but it does not provide automatic scaling capabilities to respond to changes in demand.

AWS Cost Explorer is a tool for analyzing and visualizing AWS spending patterns over time. It does not manage or scale resources based on demand.

The AWS Well-Architected Framework provides best practices and guidelines for building secure, high-performing, resilient, and efficient infrastructure for applications, but it does not offer direct scaling solutions.