title: replace blank cells in Excel with average of values before and after
body: <p>I have a time series where some records have no value 
  ex.</p>
  
  <blockquote>
    <p>A1: 1-1-2000 ------------------- B1:  2<br>
    A2: 1-2-2000 ------------------- B2:<br>
    A3: 1-3-2000 ------------------- B3:  3<br>
    A4: 1-4-2000 ------------------- B4:  6<br>
    A5: 1-5-2000 ------------------- B5:<br>
    A6: 1-6-2000 ------------------- B6:  3<br>
    A7: 1-7-2000 ------------------- B7:<br>
    A8: 1-8-2000 ------------------- B8:  7<br>
    A9: 1-9-2000 ------------------- B9:<br>
    A10: 1-10-2000 ----------------- B10:<br>
    A11: 1-11-2000 ----------------- B11: 9<br>
    A12: 1-12-2000 ------------------- B12: 8</p>
  </blockquote>
  
  <p>i need to replace blanks with the average of the values nearest before and after </p>