title: Regex for a number text combination
body: <p>sorry I'm very new to regular expressions and I need to create one that matches the following pattern:</p>
  
  <p>a number of four letters (range 2000 to 3000) , one letter (A to Z) , a number of two letters (01 to 50)</p>
  
  <p>So a valid expression would be for example: 2199R12 or 3000B01</p>
  
  <p>I have no idea how to start. Would be very happy if someone can help.</p>