[Koha] Cannot open OPAC

I installed Koha 18.11 on Ubuntu 16.04 LTS. I can open the staff client but I am getting the Apache 2 default page for OPAC. I am using port 80 for OPAC. I have tried changing the port to 81 and delete the Apache default page but I still cannot access the OPAC. Any help would be appreciated. -- Ma. Victoria H. Silva-Manuel Registered Librarian, 3892