my roslaunch command shows following error please help me out-

$ roslaunch my_mira_description simple_mira.launch model:= "$(find my_mira_description)/urdf/mira.urdf"
find: ‘my_mira_description’: No such file or directory
    Usage: roslaunch [options] [package] <filename> [arg_name:=value...]
           roslaunch [options] <filename> [<filename>...] [arg_name:=value...]

    If <filename> is a single dash ('-'), launch XML is read from standard input.

    roslaunch: error: The following input files do not exist: /urdf/mira.urdf

here is my launch file

<launch>
    <!-- use: roslaunch my_mira_description simple_mira.launch model:= "$(find myrobot_package)/urdf/myrobot.urdf"-->
    <arg name="model" default=""/>

    <param name="robot_description" command="cat $(arg model)"/>

    <!-- send fake joint value -->
    <node name="joint_state_publisher" pkg="joint_state_publisher" type="joint_state_publisher">
      <param name="use_gui" value= "TRUE"/>
    </node>

    <!-- combine joint values --> 
    <node name="joint_state_publisher" pkg="joint_state_publisher" type="state_publisher"/>

    <!-- Show in Rviz --> 
    <!-- <node name="rviz" pkg="rviz" type="rviz" args="-d $(find urdf_demo_pkg)/rviz_cfg/mira.rviz"/> -->
    <node pkg="rviz" name="rviz" type="rviz" args=""/> 

</launch>

I have the package name my_mira_description and urdf file mirla.urdf