I figure it would be a bit clearer if said as: "earth's gravity pulls down any object and if the object is stopped from falling because it is resting on the surface, or something else supported by the surface, that's what is pushing up against the object, with an equal and opposite force...
I see this as a very interesting problem, even though in some sense it is trivial. I went through the same process, being confused (momentarily) by the wording of it, yet for myself, being pretty experienced with the beat frequency effect (from having been into ham radio), the answer came...
I get the impression that the conclusion is that the question is invalid. Not necessarily so however. Since the result is dependent on the unknown mass, it likely should be presumed that the question is simply asking for a formula as an answer, with the mass as a parameter in it. One would...
Gosh, it's hard to coach this kind of a question without just giving away the answer. Maybe just study the formula for the beat frequency a lot harder, and the answer will come.