title: how to write extend network prefix?
body: <p>I need help with this: </p>
  
  <p>Assume that you have been assigned the 200.35.1.0 /24  network block
  Define an extended network prefix that allows the creation of 20 hosts on each subnet. </p>
  
  <p>I've written the addresses in binary form: 
  IP:    1100 1000 . 0010 0011 . 0000 0001 . 0000 0000
  Mask:  1111 1111 . 1111 1111 . 1111 1111 . 0000 0000</p>
  
  <p>extended network prefix must be: </p>
  
  <p>New Mask: 1111 1111 . 1111 1111 . 1111 1111 . xxxx xxxx</p>
  
  <p>I know that 2^value - 2 = subnets<br>
  But how do you know how many it requires? The subnets are not given.. Help?  </p>