Which code fragment causes a compilation error?

You are developing a banking module. You have developed a class named ccMask that has a maskcc method.
Given the code fragment:
You must ensure that the maskcc method returns a string that hides all digits of the credit card number except the four last digits (and the hyphens that separate each group of four digits).

Which two code fragments should you use at line n1, independently, to achieve this requirement?

Given:

And the code fragment:

Which code fragment, when inserted at line 14, enables the code to print Mike Found?

Given the code fragment:

Which three code fragments can be independently inserted at line n1 to enable the code to print one?

Given the code fragment from three files:

Which code fragment, when inserted at line 2, enables the code to compile?