Separate quey and parameters in sql sp_executesql

DECLARE @SQLString NVARCHAR(500)
DECLARE @ParmDefinition NVARCHAR(500)
DECLARE @IntVariable INT
DECLARE @Lastlname varchar(30)
SET @SQLString = N'SELECT @LastlnameOUT = max(lname)
                   FROM pubs.dbo.employee WHERE job_lvl = @level'
SET @ParmDefinition = N'@level tinyint,
                        @LastlnameOUT varchar(30) OUTPUT'
SET @IntVariable = 35
EXECUTE sp_executesql
@SQLString,
@ParmDefinition,
@level = @IntVariable,
@LastlnameOUT=@Lastlname OUTPUT
SELECT @Lastlname