SQL Server 2017

By using db<>fiddle, you agree to license everything you submit by Creative Commons CC0.

declare @test as table (
[Worked Hours] decimal(2,0),
[Sold Hours] decimal(3,0),
[Current Backlog] decimal(3,0),
[Product] nvarchar(10),
[Revenue Type] nvarchar(3),
[Month] date
)

INSERT INTO @TEST 
([Worked Hours], [Sold Hours], [Current Backlog], [Product], [Revenue Type], [Month])
VALUES
('10','150','50', 'BBCRM', 'T&M', '01-01-2019'),
('25','200','50', 'BBCRM', 'T&M', '02-01-2019'),
('15','175','50', 'BBCRM', 'T&M', '03-01-2019'),
('40','250','50', 'BBCRM', 'T&M', '04-01-2019');

WITH 
tab AS (
	SELECT
		t.*,
		ROW_NUMBER() OVER(ORDER BY [Month]) rn,
		COUNT(*) OVER() cnt
	FROM @test t
),
cte AS (
	SELECT 
		[Product], 
		[Revenue Type],
		[Month],
		[Worked Hours],
		[Sold Hours],
		CAST([Current Backlog] as integer) - CAST([Worked Hours] as integer) + CAST([Sold Hours] as integer) [New Backlog],
		cnt,
		1 n
	FROM tab t
	WHERE t.rn = 1
	UNION ALL
	SELECT 
		t.[Product],
		t.[Revenue Type],
		t.[Month],
		t.[Worked Hours],
		t.[Sold Hours],
		c.[New Backlog] - CAST(t.[Worked Hours] AS integer) + CAST(t.[Sold Hours] AS integer) [New Backlog],
	        t.cnt,
	        c.n + 1
	FROM tab t
	INNER JOIN cte c ON t.rn = c.n + 1
	WHERE c.n <= t.cnt
)
SELECT 
	[Product],
	[Revenue Type],
	[Month],
	[Worked Hours],
	[Sold Hours],
	[New Backlog]
FROM cte;

Product	Revenue Type	Month	Worked Hours	Sold Hours	New Backlog
BBCRM	T&M	01/01/2019 00:00:00	10	150	190
BBCRM	T&M	01/02/2019 00:00:00	25	200	365
BBCRM	T&M	01/03/2019 00:00:00	15	175	525
BBCRM	T&M	01/04/2019 00:00:00	40	250	735