Join elements in SimpleXML (PHP)

Any idea how can join and ID with another set of data and then print out certain information?
I want to print out The name and the country of a user. I am stuck already for a few hours and I would appreciate any help and suggestion!

XML:

<Project>
   <Partner>
      <PartnerRef>1</PartnerRef>
      <DaysNb>40</DaysNb>
   </Partner>
</Project>
<Partners>

 <Partner>
        <Id>1</Id>
        <Name>UNI1</Name>
        <Country>CH</Country>
    </Partner>
</Partners>

php code:

foreach($InfoSystem->xpath('//Project') as $project){
$projectId = $project->Id;
echo $projectId;
$selectedPartner = $project->xpath('//PartnerRef');
echo($selectedPartner);
echo "Title: " . $project->Submission->Title;
echo "<br>";
echo "Acronym: " . $project->Submission->Acronym;
echo "<br>";
echo "Abstract: " . $project->Submission->Abstract->Parag->Fragment;
echo "<br>";
echo $project->Submission->Abstract->List->asXML();
echo "<br>";

foreach($InfoSystem->xpath('//Partner') as $partner){

        if(in_array($partner, $selectedPartner, TRUE)){      
            echo 'Name: ' . $partner->Name;
            echo 'Country: ' . $partner->Country;
        }
   
    

    echo $partner->Id;
   
       
    
}

echo "<br><br>";

}