Man, it feels like it's been forever since I last made a post here. [More like several months or what have you.] And yet, here I am with a different issue. 
I'm not quite sure why my mom is getting this error during her update process, but it's got me somewhat puzzled too. 
I tried doing some Googling earlier to find out some answers, but I've yet to find a solution/explanation that is easy to understand. I'm including 3 screenshots btw. 1 is the exact error message received in the terminal during updates & the other 2 are showing the settings for both the Ubuntu Software & Other Software within the Software & Updates tab/app.
So anyway, I'm hoping someone here can help me resolve this issue. If any of you happen to need more details, or have questions, please be sure to ask & I will reply back! 
** Also, spoiler alert: I myself don't daily-drive Linux & I don't really know everything about it, but I'm more FAR more knowledgeable than my mom since that's why I take care of her pc's maintenance duties. ** Also, if there's anything I should actually change DO let me know!
Thanks in advance to anyone whom can help! 