You need to parse the string into a numeric datatype and then multiply this by ten and format this data type:
Dim stringValue As String = "-1.80"
Dim doubleValue As Double
Dim outputString As String
If Double.TryParse(stringValue, doubleValue) Then
outputString = (doubleValue * 10).ToString("0.00")
Else
Throw New Exception("Value could not be parsed")
End If
Debug.WriteLine(outputString)
This will work with both negative and positive numbers