Your question is Facebook Page Follow Recommender. Take a moment with it on the right.
Talk me through your thinking if you like. When you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes).
Design facebook recommender for page follow.
Clarify the product objective, scale, and definition of a successful follow recommendation. Propose an end-to-end system covering candidate retrieval, ranking, re-ranking, serving, training data, evaluation, and failure handling.