Mint update errors ???

[joe at actionline.com]

When I last tried to update a Dell laptop,
I got these errors. How can I fix this?

E: /var/cache/apt/archives/mint-artwork-common_1.8.1.2_all.deb: subprocess
dpkg-deb --control returned error exit status 2

W: Failed to fetch
http://packages.linuxmint.com/pool/upstream/f/firefox/firefox_60.0.1+linuxmint1+rosa_amd64.deb
  404  Not Found [IP: 68.235.39.11 80]

W: Failed to fetch
http://packages.linuxmint.com/pool/upstream/f/firefox/firefox-locale-en_60.0.1+linuxmint1+rosa_amd64.deb
  404  Not Found [IP: 68.235.39.11 80]

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