Order by two meta values - one is a number and the other is text

Based on multiple searches, this is the code I'm trying to sort by two different meta key values.

'meta_query' = array(
        'relation' = 'AND',
        'listing_order' = array(
            'key' = 'atsc_bod_listing_order',
            'compare' = 'EXISTS',
        ),
        'last_name' = array(
            'key' = 'atsc_bod_last_name',
            'compare' = 'EXISTS',
        ), 
    ),
    'orderby' = array( 
        'listing_order' = 'ASC',
        'last_name' = 'ASC',
),

I want to first sort by a numerical value and then if the numerical values are the same, sort by last name. This code returns no results. I'm think it has something to do with not knowing if the sort field is 'meta_value_num' or 'meta_value' but I'm not sure how/where to add that information.

Here is the full code that includes the suggestion below.

?php
        $args = array (
        'post_type'         = 'atsc_bod',
        'posts_per_page'    = -1,
        'post_status'       = 'publish',



            'meta_query' = array(
                    'relation' = 'AND',
                    'listing_order' = array(
                        'key' = 'atsc_bod_listing_order',
                        'compare' = 'EXISTS',
                        'type'    = 'NUMERIC',
                    ),
                    'last_name' = array(
                        'key' = 'atsc_bod_last_name',
                        'compare' = 'EXISTS',
                    ), 
                ),
                'orderby' = array( 
                    'listing_order' = 'ASC',
                    'last_name' = 'ASC',
            ),



        );
        $loop = new WP_Query($args);
        ?