Answer: String Data
Explanation: In Javascript, the prompt() method is used to display a dialog that prompts you to insert an optional message which is basically some text.
The text can be textual, numerical (as in your example) or both but all this line of the program (line 2) is trying to do is to get data from the user.
It returns a STRING containing the text entered by the user, or null.
Note: The string that is returned cannot be used directly to solve any math until you convert it to an integer. That's what line 3 is for.