title: convert String containing a arithmetic sign into a integer value
body: <pre><code>    String a = "a*3";
      a = a.replace("a","45");
  
      // a contains 45*3
  </code></pre>
  
  <p>How do you I convert that to a DOUBLE which outputs 135.00 ??</p>
  
  <p>Note : a can have any arthimetic operation... ( + , - , /)</p>