Average Monthly Spend and Forecast

Hello,

I am new to PowerBI so I could use some assistance:

I have a table that contains invoice data with the date received and the amount of the invoice.  I would like to do two things:

1. Find the average amount spent per month, year over year (Average of July 2012, July 2013, July 2014).

2. Use these averages to fill in missing data for spending forecasts - As of this writing it is November 2nd.  So based on the average Novemeber and December invoice data what is the total expected spend for the year.

Table

Thank you for any help you can provide,

Matt