SQL weight multiplication Hi all i have two columns in a table : 

+--------------------+----------------+
| Units/Pk           | PackWeight/Vol |
+--------------------+----------------+
| 1.0000000000000000 | 150g           |
+--------------------+----------------+
| 1.0000000000000000 | 150g           |
+--------------------+----------------+
| 1.0000000000000000 | 114g           |
+--------------------+----------------+
| 1.0000000000000000 | 500g           |
+--------------------+----------------+
| 1.0000000000000000 | 200g           |
+--------------------+----------------+
| 1.0000000000000000 | 500g           |
+--------------------+----------------+
| 1.0000000000000000 | 500g           |
+--------------------+----------------+
| 1.0000000000000000 | 200g           |
+--------------------+----------------+
| 1.0000000000000000 | 200g           |
+--------------------+----------------+
| 4.0000000000000000 | 100g           |
+--------------------+----------------+
| 4.0000000000000000 | 125g           |
+--------------------+----------------+
| 4.0000000000000000 | 125g           |
+--------------------+----------------+
| 1.0000000000000000 | 500g           |
+--------------------+----------------+


I need to multiply these together for result to replace values in PackWeight/Vol i.e. Units/Pk * PackWeight/Vol AS PackWeight/Vol.  How do i do this?  i.e. where units is 4 result would be 400g, 500g, 500g respectfully.  Other results would stay the same as units are 1.  Units/Pk is numeric and packweight is nvarchar. Thanks!
This is one way to accomplish this, but I agree with JNK in the comments that it will scale very poorly and perform the same:

    SELECT CASE WHEN ISNULL([PackWeight/Vol], '') = '' OR PATINDEX('%[a-Z]%', [PackWeight/Vol]) = 0 
THEN '' 
ELSE CAST(SUBSTRING([PackWeight/Vol], 1, PATINDEX('%[a-Z]%', [PackWeight/Vol]) - 1)  * [Units/Pk] AS VARCHAR(256)) + 
               SUBSTRING([PackWeight/Vol], PATINDEX('%[a-Z]%', [PackWeight/Vol]),  LEN([PackWeight/Vol]) + 1 - PATINDEX('%[a-Z]%', [PackWeight/Vol]))
    END
        FROM table