Trouble using R Markdown

Hi Everyone. I am trying to use RMarkdown to complete an assignment, and every time I press the knit button to see the code I have saved, it says error. Any idea how I can fix this?

When you knit a document your code gets executed on a clean environment (where rent.US doesn't exist) so you have to include the code for reading this dataframe into your Rmd file.

How would I do that?

Just type the same commands you used to get rent.US into your current environment.