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!