Two ReplicaSet manifests are in ~/plains-zb90e1. Apply the first one into plains-zb90e1:

kubectl apply -f ~/plains-zb90e1/web-rs.yaml -n plains-zb90e1

Watch kubectl get rs,pods -n plains-zb90e1 until three Pods are Running. Delete one and count again. Scale the ReplicaSet to 5.

Then apply api-rs.yaml. It is refused. Read the message, fix the file, apply again.