How to install armhf package on ubuntu 18.04 Bionic Beaver

I’m trying to install Opencv on ODROID XU4 ARM platform where I’m following this tutorial https://www.learnopencv.com/install-opencv-4-on-ubuntu-18-04/. I am using ubuntu 18.04 Bionic Beaver(32 bits). when I try to add the repository for updates I get the following error problem with armhf package, and when I open etc/apt/source.list I get this script source.list`

Can you please help with this problem ? why do I have problem with downloading armfh package ?