title: Create a new column in R spreadsheet with a specific calculation
body: <p>I have looked for an answer to this on stackexchange but the questions being asked are way more complicated than what I need. </p>
  
  <p>I have a table in R </p>
  
  <pre><code>Teacher Name  Usage_in_MINS  Usage Rate
        Kelper             78 
        Kelper             85
         Smith             85
        Kelper             45
         Smith             65
     7th Grade             45
     4th Grade             34
  </code></pre>
  
  <p>How do I get R to create a new column called <code>Usage Rate</code>
  How do I get this new column to take the values in <code>Usage_in_MINS</code> and divide it by 60 for only those classes that are either <code>Kelper</code> or <code>Smith</code>? What about if I want it to calculate usage rates for <code>Kelper</code> and <code>Smith</code> and everyone else as well.</p>