Fact table rows calls with average number for all calls

Computer Science
Write a query that returns individual row results from the fact table, but also returns the average for all the rows and for each shift using the OVER command. In your query, use those results to calculate the difference between a fact table rows’s Calls with the average number for all the calls. Here is a sample of the result set:

FactCallCenterID	Shift	Calls	FullDateAlternateKey	AvgforAllCalls	AvgforShiftCalls	Difference
91	PM2	699	2010-11-23	361	512	338
95	PM2	669	2010-11-24	361	512	308
79	PM2	663	2010-11-20	361	512	302
51	PM2	648	2010-11-13	361	512	287
115	PM2	632	2010-11-29	361	512	271