In the atttached workbook, I have supplied a few modifications to assist.
1 - A date field with the fields supplied to get a monthly value - Date([Month]+"/1/"+[Year])
2 - A running sum of SumOfMarketView=S= RUNNING_SUM(SUM([SumOfMarket View =S=]))
3 - Difference betwen Y Target and the running sum as Remaining Target
4 - and then the Avg to hit when the Y- Target-Running Sum value is calculated per month. - This is the right most column in the attached workbook.
I have saved this workbook in version 9.3 which is new as of last week. You can find 9.3 here Alternate Downloads Site | Tableau Software .
I went ahead and modified the source data to show this in a bit more detail with no more sales for sum of market view yet the remaining avg per month shown to hit target for 2016 as I thought i tmight help to see all of the other months in a view.