Add an 'Average' line to line chart

I have a line chart that works great …

Screen Shot 2020-07-08 at 11.46.58 AM875×305 20.8 KB

What I want to do is add a second line for the average. I know I must do that in my query but can’t figure out the proper syntax. Here is my Query …

SELECT
	joborders.JODateRec AS Work_Date,
	COUNT( joborders.JODateRec ) AS Job_Orders
FROM
	joborders 
WHERE
	joborders.JODateRec >= NOW() - INTERVAL 28 DAY 
GROUP BY
	joborders.JODateRec 
ORDER BY
	joborders.JODateRec