The art instructor must purchase no fewer than 8 sets of 8 brushes. Each set contains 8 brushes, and since she requires AT LEAST 60, it is essential that she acquires at least that quantity, although more can be added. By buying 8 sets, she would end up with 64 brushes, giving her an excess of 4 brushes. Thus, securing 8 sets guarantees she meets the minimum requirement of 60 brushes.
