You can use a long text field and tell users what to do in the help text. However, it will be up to the users to follow the instructions.
If you want to be sure that the user enters three values, you could use three single line text fields and make them all required. Even so, you are still at the mercy of users following instructions because they could enter the same thing three times or other nonsense.
There is no way to enforce a specific answer structure and also have user defined text.
That text could be pre-filled into the long text field, but the user would be free to delete it if they wish. It sounds like three individual text fields would be a better way to go. You can change the labels in the form view so they differ from the actual field names, and include help text if you feel it would be useful. Perhaps make the first field required and the second two optional.