Which additional step should the solutions architect take?

Explanations:

While migrating to Amazon RDS for MySQL with a cross-Region read replica can improve availability and reduce latency for reads in us-west-2, it does not satisfy the RTO and RPO requirements effectively. Cross-Region read replicas have inherent latency and can take time to promote to master during a failover, which could exceed the RTO of 5 minutes.

Migrating to an Amazon Aurora global database allows for cross-Region replication with an RPO of less than 1 minute and supports fast failover capabilities, thereby meeting the RTO requirement. This setup enables the secondary database in us-west-2 to be promoted to primary with minimal downtime, ensuring the application remains available.

An Amazon RDS for MySQL Multi-AZ deployment provides high availability within a single Region, but it does not support cross-Region failover or replication. In a disaster recovery scenario requiring a failover to us-west-2, this option would not meet the RTO and RPO requirements, as it lacks the necessary cross-Region replication features.

Creating a MySQL standby database on an EC2 instance in us-west-2 would require manual intervention for failover, which could lead to an RTO exceeding 5 minutes. Additionally, managing the replication and ensuring the RPO of less than 1 minute would be complex and error-prone compared to using managed database solutions like Aurora or RDS.