Display:

$\underset{\_}{(}\frac{a}{b}\stackrel{\‾}{)}$

Source:

<mrow>
     <munder>
          <mo> ( </mo>
          <mo> &UnderBar; </mo>
     </munder>
     <mfrac>
          <mi> a </mi>
          <mi> b </mi>
     </mfrac>
     <mover>
          <mo> ) </mo>
          <mo> &OverBar; </mo>
     </mover>
</mrow>