Analyse and check further, CONVERT() function converts to the required type, For arithmetic operations we would need it to be either Integer or Double, we could specify the required type just like you have specified ‘System.String’. Also the Multiplication(*10) applies after the conversion.
Do also closely observe the syntax, there are Open and Closing brackets mismatch.
Do let us know if you were able to correct this last segment.
Is the Original Topic answered ? We would like to Scope the Topic for One Question/Topic, so that it is properly visualised for other users the Question/Query and the Solution, so that we also maintain the Thread Length.
Newer Topics could be created for separate queries, we can provide separate answers for it.
Regarding your last query, do analyse further (always), as you are using a variable, you should not add it within the Column Expression but after the Column Expression ends. But also enclose it within Single Quotes. As you can notice, when just the name of the Variable is added to the expression, it is just a String value and not the variable value.
You can create separate topic on this query so a better/more individual help could be provided to that.