A Line of Best Fit is called a Trendline in Google Sheets. To add a Trendline to your Line Chart: Go to Chart Editor > Customize > Series > Scroll down and click on the tick box for Trendline.

Adding a graph in a spreadsheet is no big deal as long as you know the process. However, do you know that you can make a curved line graph in Excel or Google Sheets? If not, you should check out ...