SO_44127469, Php - rextester

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<?php //php 7.0.8
    
    $arrayData = array(
    "q1" => 4,"q2" => 4,"q3" => 8,"q4" => 6,"q5" => 12,"q6" => 2
    );
     $targetSUM = 16;
    //First of all, remove any doubt and see 
    //if the sum of the entire array is the same as our target
    
    if($targetSUM === array_sum($arrayData)){
        print_r($arrayData);
        die();
    }
    $i=0;
    $results = array();
    foreach($arrayData as $questionA=>$markA){
        
        $thisCycle = array($questionA=>$markA);
        foreach($arrayData as $questionB=>$markB){
            if ($questionA === $questionB) continue; // avoid sum SUM itself
           
            $thisCycle[$questionB] = $markB;
            
            $thisCycleSUM = array_sum($thisCycle);
            
            switch(true){
                case $thisCycleSUM < $targetSUM: //if results not reach our target, go on
                    continue;
                break;
                case $thisCycleSUM === $targetSUM: //if results match, store and go on
                   $results[$i] = $thisCycle;
                   $thisCycle = array($questionA=>$markA);
                break;
                case $thisCycleSUM > $targetSUM: //if results exceeds, remove last element and go on
                    unset($thisCycle[$questionB]);
                break;
            }
                
        }
        // Sorting procedure to avoid the same combinations
            ksort($results[$i]); 
            $results[implode(array_keys($results[$i]))] = $results[$i];
            unset($results[$i]);
            $i++;
        
    }
        $results = array_values($results);
       print_r($results);
?>

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