I'm not able to launch my robot on arena in gazebo.. ros-melodic

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Hello.

I want to launch my robot on an arena in gazebo simulation. I had launched the robot and the arena in the simulation, but the problem which I am facing is the arena is being launched on top of the robot instead of launching the other way around which is robot on arena at a particular location. 
This is my launch file code:

<?xml version="1.0" encoding="UTF-8"?>
<launch>
    <include file="$(find gazebo_ros)/launch/empty_world.launch"/>
    <param name="robot_description" command="cat '$(find beginner_tutorials)/urdf/arena.urdf'" />
    <include file="$(find beginner_tutorials)/launch/my_robot.launch"/>
  <arg name="yaw" default="0"/>
  <arg name="pitch" default="0"/>
  <arg name="roll" default="-90"/>
  <arg name="x" default="6"/>
  <arg name="y" default="6.5"/>
  <arg name="z" default="0"/>
    <node name="arena" pkg="gazebo_ros" type="spawn_model" output="screen"
        args="-file $(find beginner_tutorials)/urdf/arena.urdf -urdf -model arena -Y $(arg yaw) -P $(arg pitch) -R 
$(arg roll) -x $(arg x) -y $(arg y) -z $(arg z)"/>
</launch>

Please help me to solve this problem.
Thank you.