title: Interpolation on excel
body: <p>I've a source data like this:</p>
  
  <pre><code>       35    40
  -15    15.0  15.1
  -10    17.2  17.4
  -5     19.7  19.8
  </code></pre>
  
  <p>and I need to find the value in (-16, 37). I've tried with linear interpolation but I can solve only with (x,y) couple of values. Could you help me?</p>
  
  <p>thanks a lot,
  Andrea</p>