Order Value per Region

Please assist. I would like to answer this question: "What is the average order value in the African Region per month?"

My Data Model(https://drive.google.com/file/d/1mXQpAl_m02ZtGzxNk2L_vFPCySzMR7qh/view?usp=sharing)

sample-data-tpch-schema

My Code:

SELECT Avg(Orders) AS Order Value

FROM Orders, Customer, Nation, Region

Join Customer AS C

ON Customer.Custkey = Orders.Custkey

Join Customer AS C ON Customer.Nationkey=Nation.Nationkey

Join Nation.Nationkey=Region.Nationkey

where Region = Africa