Here is the example:

ComboChart::create(array(
    "columns"=>array(
        "category",
        "dataBar",
        "dataLine"
    ),
    "options"=>array(
        "series"=>array(
            array("type"=>"bars"),
            array("type"=>"line"),
        )
    )
));

Above code show you the most important code to setup a combochart, however you will need data which is required for any charts, for example

<?php
ComboChart::create(array(
    "dataSource"=>array(
        array("category","dataBar","dataLine"),
        array("Pencil",50,100),
        array("Paper",30,50),
        array("Book",120,30),
    ),
    "columns"=>array(
        "category",
        "dataBar",
        "dataLine"
    ),
    "options"=>array(
        "series"=>array(
            array("type"=>"bars"),
            array("type"=>"line"),
        )
    )
));
?>

For the purpose of demonstrating ComboBox, I use the array as datasource.