concat dts variables

Hello,

i know its a rela noob Question, but i didnt find a solution:

Public Sub Main()
		'
		' Add your code here
        '
            Dts.Variables["user::sql"].Value = Dts.Variables["sqlVorlage"].Value & ToString,Dts.Variables["lastdate"].Value;
		Dts.TaskResult = ScriptResults.Success
	End Sub

Error 1 Property access must assign to the property or use its value

and

Error 2 Identifier expected.

What is wrong? I want to concat the two string values

greetings