Figure is an overhead view of a 12 kg tire that is to be pulled by three

Question:

Figure is an overhead view of a 12 kg tire that is to be pulled by three horizontal ropes. One rope's force (F1 = 50 N) is indicated. The forces from the other ropes are to be oriented such that the tire's acceleration magnitude a is least. What is that least a if?

(a) F2 = 30N, F3 = 20 N;

(b) F2 = 30N, F3 = 10N; and