title: Transform string into an arithmetic operation
body: <p>I have this string:</p>
  <pre><code>x = &quot;2x4, 2x5&quot;
  </code></pre>
  <p>I want to transform it into the following operation:</p>
  <pre><code>x = (2 * 4) + (2 * 5)
  </code></pre>
  <p>So the final result will be 18.</p>
  <p>Do you have any idea ? If the solution can be flexible to strings with different number of items (ex: &quot;2x4, 2x5, 2x7&quot;) it would be great !</p>
  <p>Thanks !</p>