SQL to get last 4 quarter sum total

Hi Guys

I've got some SQL skill but this one has me thrown. I have a FACT table with Partner_Key, QuarterName and Total_Assets. Finance_Id is the primary key:

CREATE TABLE [dbo].[Fact_FINANCE](
    [Finance_ID] [int] NOT NULL,
    [Partner_Key] [int] NOT NULL,
    [QuarterName] [varchar](6) NOT NULL,
    [Total_Assets] [decimal](15, 2) NOT NULL

)

The data looks as follows:

• 1,9,2015Q1,1500
• 2,9,2015Q2,1000
• 3,9,2015Q3,2500
• 4,9,2015Q4,900
• 5,9,2016Q1,2400
• 6,9,2016Q2,1600
• 7,9,2016Q3,1000
• 8,9,2016Q4,1200

I would like a query that returns the current quarter with the sum of the current and previous 3 quarters in one line:

• Partner_Key: 9
• QuarterName: 2016Q4
• Sum(Total_Assets): 1200 + 1000 + 1600 + 2400 = 6200

The total for 2016Q3 would then be 1000 + 1600 + 2400 + 900 = 5900

Any advice for me?

Thanks!