I need help with adding trendline and finding the r squared value

[vamihe30]

For my biology class, I had to conduct an experiment and put down all my information on excel. I had to put in all the data and create a scatter plot, after i did that I had to add a trendline and then find the r squared value. I don't know if I'm doing it wrong or something is wrong with my version of excel, but I desperately need help.

[#2]

@vamihe30 Add a trend line by selecting any data point. On the "Chart design" ribbon, look for the button shown (Add chart element) in the picture below to add the trend line.

Once you have added the trend line, click on it and a "Format Trendline" window will appear. Select "display R-squared value on chart" at the bottom. 

[#3]

@Riny_van_Eekelen 

 Mine doesn't give me that option at all. It only says "chart" 

[#4]

@Erica_Roberson You're working in Excel for the Web. Trendlines can't be added or edited on that platform. But you can create your chart in the desktop version. The trendline and R2 will show in the on-line version. They will change as your data changes, but as said, you can't edit them.