<?xml version="1.0" encoding="UTF-8"?>
<math xmlns="http://www.w3.org/1998/Math/MathML">
   <mi>S</mi>
   <mfenced close=")" open="(">
      <mi>x</mi>
   </mfenced>
   <mo>=</mo>
   <mn>3</mn>
   <mi>x</mi>
   <mo>+</mo>
   <mn>1</mn>
</math>
