Here is one approach. It assumes you have an "Answer" style in your document to apply to the correct answers. You can then have a secondary macro that toggles the "Answer" style as being same/different to the Normal style if you wanted to show or hide the answers.
Code:
Sub MarkAnswers()
Dim lngPara As Long, iOffset As Integer, sAnswer As String
For lngPara = 1 To ActiveDocument.Paragraphs.Count
If Left(ActiveDocument.Paragraphs(lngPara).Range.Text, 5) = "Ans: " Then
sAnswer = ActiveDocument.Paragraphs(lngPara).Range.Words(3)
iOffset = Asc(sAnswer) - 69
Debug.Print lngPara, sAnswer, iOffset
ActiveDocument.Paragraphs(lngPara + iOffset).Range.Style = "Answer"
End If
Next lngPara
End Sub
Sub ToggleAnswerShow()
Dim aSty As Style
With ActiveDocument.Styles("Answer")
If .Font.Bold = ActiveDocument.Styles("Normal").Font.Bold Then
.Font.Bold = True
.Font.ColorIndex = wdGreen
Else
.Font = ActiveDocument.Styles("Normal").Font
End If
End With
End Sub