Need help with this array, everything works fine excpt the last line im not getting the values on `$data[5][1] + $data[1][2] - $data[2][2]` ,

```
$data = array(
    array("Concepto","Enero","Febrero","Marzo","Abril"),
    array("Ingresos",100,       100,    100,    100),
    array("Egresos",200,        200,    200,    200),
    array("Deudores",300,       300,    300,    300),
);

$aa = array("Saldo",($data[1][1]-$data[2][1]),($data[1][2]-$data[2][2]),($data[1][3]-$data[2][3]),$data[1][4]-$data[2][4]);
array_push($data,$aa);
$bb = array("Saldo Acumulado",(5000)+($data[1][1])-$data[2][1],
            $data[5][1] + $data[1][2] - $data[2][2],
            "3",
            "4");
array_push($data,$bb);

$tblCuatrimestre1 = '<table width="100%" border="0" cellspacing="0" cellpadding="0">';
foreach($data as $dat){
      $tblCuatrimestre1 .= ' <tr>
        <td width="20%">'.$dat[0].'</td>
        <td width="20%">'.$dat[1].'</td>
        <td width="20%">'.$dat[2].'</td>
        <td width="20%">'.$dat[3].'</td>
        <td width="20%">'.$dat[4].'</td>
        <td width="20%">'.$dat[5].'</td>
      </tr>';
}
$tblCuatrimestre1 .= '</table>';
echo $tblCuatrimestre1;

```