First thing I thought lmao. Somebody is taking logic

Honestly what the homework is probably looking for is that it's equivalent to "B or not A." But yeah.

Edit: I see the error in my below response. I leave wrong answers for conversational completeness

That's not equivalent either. "if not b, then not a" works if it's a sequence but doesn't work for options in which multiple inputs can lead to the same output. If you get pizza every Tuesday and Friday, then answering "what's for lunch" with "if Tuesday, then pizza" and "if Friday, then pizza" doesn't let it work in reverse. "what day is it" can't be answered with "if pizza lunch, then Tuesday"