Is there a way to find the average of a php variable from a database table?

Question

I am trying to generate an average line on my line chart.

I tried the following code but it is not working, i would like to plot the average of $tit.

How can i alter my code to achieve this.

<script type="text/javascript">
    google.charts.load('current', {
      'packages': ['corechart']
    });
    google.charts.setOnLoadCallback(drawChart);

    function drawChart() {
      var data = google.visualization.arrayToDataTable([
        ['id', 'TIT','Average'],
        <?php
        $query = "select id,tit1,avg(tit1) as average_tit from engine2";
        $res = mysqli_query($conn, $query);
        while ($data = mysqli_fetch_array($res)) {
          $id = $data["id"];
          $tit = $data["tit1"];
          $avg = $data["average_tit"];
          
          
        ?>
          ['<?php echo $id; ?>', <?php echo $tit; ?>, <?php echo $avg; ?>],
        
        <?php 
      } 
      ?>
      ]);

      var options = {
        title: 'T5',
        // curveType: 'function',
        legend: {
          position: 'bottom'
        }
      };

      var chart = new google.visualization.LineChart(document.getElementById('curve_chart3'));

      chart.draw(data, options);
    }
  </script>

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