I will assume that you've solved the previous questions correctly.
Steps:
Create a new query using "Query Design"
add the four tables
add the fields: Forename, surname, cost and CustRef from the table J9cust.
click the "Sigma symbol" to show totals.
under custref's criteria, write ">1" and change "Group by" to "Count" (Select from all the records only the customers that have booked more than one holiday). CustRef is unique for every customer.
from the dropdown list of totals of "Cost", choose Avg (average).
Save your query.
Create a new report using report wizard.
choose your query and the four fields
click next.
group the data by "CountofCustRef"
click next, sory data into ascending order of surname and then ascending order of forename.
Change page layout to landscape.
click finish.
go to report's design view.
click on group and sort, and choose to show CountofCustRef Footer.
in the countofcustref footer, add a text box and paste "=avg[avgofcost]"
add your name/centre number.
Done
I've attached my working files, use them.