Which solution will meet these requirements?

Explanations:

Reducing the number of application servers could impact the availability of the application, especially since it runs across three instances for redundancy. This approach may save costs but is not aligned with the requirement of maintaining application availability.

Applying rightsizing recommendations from AWS Cost Explorer can optimize costs by reducing the instance size without affecting the application’s performance or availability. This approach ensures that resources are better aligned with actual usage, potentially lowering costs while maintaining the required performance.

Provisioning an Application Load Balancer would likely increase costs due to the additional resources required for load balancing. While it improves availability and scalability, it does not directly address the issue of low utilization or reduce costs effectively in this scenario.

Scaling up the instance size of the application servers would increase costs, which contradicts the goal of reducing expenses. This option does not address the low utilization problem, as increasing instance sizes generally implies higher resource allocation without improving utilization rates.