Linq to XML, select query with where condition

This is my XML content:

<ListEnginsMesures>
    <EnginsESC>
      <NomValide>Engin_inconnu</NomValide>
      <NomEquivalents>
        <NomEquivalent>Engin inconnu</NomEquivalent>
        <NomEquivalent>Engininconnu</NomEquivalent>
      </NomEquivalents>
    </EnginsESC>
    <EnginsESC>
      <NomValide>DRSC_6150</NomValide>
      <NomEquivalents>
        <NomEquivalent>DRSC 6150</NomEquivalent>
        <NomEquivalent>DRSC6150</NomEquivalent>
        <NomEquivalent>DRSC6.150</NomEquivalent>
        <NomEquivalent>DRSC_6.150</NomEquivalent>
      </NomEquivalents>
    </EnginsESC>
<ListEnginsMesures>

I want to select value of 'NomValide' when i have 'NomEquivalent'.

For example :

(select 'NomValide' where 'NomEquivalent' = "Engin inconnu") will return Engin_inconnu.

(select 'NomValide' where 'NomEquivalent' = "DRSC_6.150") will return DRSC_6150.

HOW CAN I ACHIEVE THIS ONE ?

THANKS IN ADVANCE..