HI Ive got this question I dont know how to do;

Let X be a metric space, and let Q,J be non-empty subsets of X. prove that

inf{dist(x,J):x is a member of Q}= inf{dist(Q,y):y is a member of J}.

I know that the dist(x,J):= inf{d(x,y)|y is a member of J}, but I am not sure how to tackle this question. Any help please?