This is from page 106 of The Complete Elementary Music Rudiments, 2nd Edition by Mark Sarnecki. It is in the section about enharmonic intervals
The question is asking for the interval from A# to E# (a perfect 5th), after the A# is changed enharmonically. The only notes enharmonic to A# are Bb and Cbb, and they would result in a double-augmented-4th or a triple-augmented-3rd, which aren't really proper intervals and were never mentioned in the book.
Is this a publication error? Or am I missing something?