SQL Server查询某个日期段内的平均值

DECLARE @SampleOrderTable TABLE
                          (
                               pkPersonID INT,
                               OrderDate DATETIME,
                               Amount NUMERIC(18, 6)
                          )

INSERT INTO @SampleOrderTable (pkPersonID, OrderDate, Amount) 
VALUES (1, '12/10/2019', '762.84'),
       (2, '11/10/2019', '886.32'),
       (3, '11/9/2019', '10245.00')

如何选择之前的最后4天OrderDate以及该期间的平均金额？

因此结果数据将是：

pkPersonID   Date             Amount
------------------------------------
    1        '12/7/2019'     190.71
    1        '12/8/2019'     190.71
    1        '12/9/2019'     190.71
    1        '12/10/2019'    190.71
    2        '12/7/2019'     221.58
    2        '12/8/2019'     221.58
    2        '12/9/2019'     221.58
    2        '12/10/2019'    221.58
    3        '11/6/2019'    2561.25
    3        '11/7/2019'    2561.25
    3        '11/8/2019'    2561.25
    3        '11/9/2019'    2561.25