title: How to remove string between parentheses
body: <p>I try to find the right expression to remove some strings in my Google Spreadsheet. I have lot of cells based on this model : </p>
  
  <pre><code>15.01 km2 (5.80 sq mi)
  </code></pre>
  
  <p>I want to remove all the text from <code>km2</code> for this result: <code>15.01</code>.</p>
  
  <p>I've tried LEFT function but it cannot be based on a text. I guess it can be achieved using REGEXEXTRACT.</p>