SQL Server 2008 :: How To Divide Value In Row 1 By The Value In Row 2 In Same Column

I try to take the value from row 1 divided by the value from row 2 but it is not working, here is the following:

Here is my table called Trans

ID Period Sales Profit
1 Current 20 5
2 Previous 40 20

I want to take 20 divided by 40(20/40), 5 divided by 20(5/20)

Here is the result I want:

ID Period Sales Sales_Per Profit Profit_Per
1 Current 20 50% 5 25%
2 Previous 40 50% 20 25%

Here is my query:

Select
(t1.Sales/NULLIF(t2.Sales,0) * 100) as Sales_Per
From Trans t1
INNER JOIN Trans t2
on t1.Id = t2.ID - 1