Error converting data type nvarchar to numeric.

Hi Sap Experts

Please can you advise if there is a formula to convert the data type from nvarchar to numeric.

I have raised a formatted search but when the quantity is separated by a comma at thousand I get the below error message.  My query is as per the below

'Error converting data type nvarchar to numeric.'

SELECT (T0.IWeight1 * $[$-38.11]) FROM OITM T0 WHERE $[$-38.1]=t0.itemcode

Many Thanks

Chris