Working alone, machine X can manufacture 1,000 nails in 12 hours. Working together, machines X and Y can manufacture 1,000 nails in 4 hours. How many hours does it take machine Y to manufacture 1,000 nails working alone?  Choose the correct answer:
A) 3 9/17	B) 6	C) 7	D) 7 1/5	E) 8 4/7
rate of machine x = 1000/12   (1000/12 + y)4=1000   y=350/3   500/3 * t = 1000   t=6   6.
<result>B</result>
Working alone, machine X can manufacture 1,000 nails in 12 hours. Working together, machines X and Y can manufacture 1,000 nails in 4 hours. How many hours does it take machine Y to manufacture 1,000 nails working alone?