If it's not a well written case, the interviewer probably wants to simply test your logic.

In this case, think about the individual components of ROE - (i) Returns and (ii) Equity.

- Returns: if you own your own stores, revenues will be higher (but so will the costs). On the contrary, under a franchise model you will only be paid royalties - but those will go straight to profits (i.e. little costs associated)

- Equity: owning your own stores will require a larger upfront investment and continuous maintenance vs. operating a franchise model. Hence, more equity needs to be invested in the business

In your example, Company B (Starbucks) operates its own stores (which requires more capital) and yet has lower revenues. Moreover, the margins it earns on this revenues are relatively lower than Company A (because of the franchise model point above).

So, keeping things as simple as possible, it's fair to say that its ROE is expected to be lower.