title: Got knit issue with R
body: <p><a href="https://i.stack.imgur.com/Rp22I.jpg" rel="nofollow noreferrer">my code is working but I can not knit that part,Quitting from lines 17-19 (Homework-template.Rmd)
  Error in data.frame(Davis$weight) : ÕÒ²»µ½¶ÔÏó'Davis'
  Calls:  ... withCallingHandlers -&gt; withVisible -&gt; eval -&gt; eval -&gt; data.frame
  ´ËÍâ: Warning message:
  In has_crop_tools() :
  Tool(s) not installed or not in PATH: pdfcrop, ghostcript
  -&gt; As a result, figure cropping will be disabled.</a></p>