Ugh, R... I don't know why life is so difficult with it... But anyways...
Can you please try copy+pasting each of these lines? (I would copy+paste the first one, and you will be asked for your administrative password, and then you can copy+paste the others all at once, if you want, and the admin password will be saved to apply to the others for a short interval):
sudo add-apt-repository -y "ppa:marutter/rrutter3.5"
sudo add-apt-repository -y "ppa:marutter/c2d4u3.5"
sudo apt update
sudo apt install -y r-cran-brms
--pt
