Hiroyuki Appliance uses a perpetual inventory system. For its flat-screen television sets, the January 1 inventory was 4 sets at $636 each. On January 10, Hiroyuki purchased 6 units at $694 each. The company sold 3 units on January 8 and 5 units on January 15. Calculate moving average cost at January 1, 8, 10 & 15.