Yes it is possible.
Fetch data using mysqli_fetch_assoc
and then iterate through the diferent keys of the array (each row is an array).
Will be something like this:
$conn= mysqli_connect("mydbhost", "my_user", "my_password", "mydatabase");
$result= mysqli_query($conn, "SELECT rs_turista, rs_nocenja, agencija_turista, agencija_nocenja, at_turista, at_nocenja, be_turista FROM mytable");
$ttl= 0;
while ($row = mysqli_fetch_assoc($result)) {
foreach($row as $key => $value) {
$ttl += $value;
}
}
echo $ttl;
$mysqli_close($conn);
Of course, you need to do some error checking on connection, but at last, the basic schema is like this.
Look at here for more information: http://php.net/manual/en/mysqli-result.fetch-assoc.php