Ubuntu 18.04 with kubuntu /Plasma enable numlock on login

Hi I went through a lot of solutions and tried a couple of them. But till so far no progress.

1. I went through Activating numlock on bootup – ArchWiki without succes.

2. I installed numlockx sudo apt install numlockx. No erorrs.

3. Followed by sudo sed -i 's|^exit 0.*s|# Numlock enablen[ -x /usr/bin/numlockx ] && numlockx onnnexit 0|' /etc/rc.local

Then I got this error (translated from Dutch into English)

sed: cannot read /etc/rc.local :file or folder does not exist.

I am looking forward if someone could give me the right command line instruction to enable Numlock on login.

plasmashell 5.12.9

Qt: 5.9.5

KDE Frameworks: 5.44.0

kf5-config: 1.0