X can do a piece of work in 4 hours; Y and Z together can do it in 3 hours, while X and Z together can do it in 2 hours. How long will Y alone take to do it? Choose one.
A) 5hours	B) 10hours	C) 12hours	D) 24hours	E) 15hours
X 1 hour's work =	1/4	;   Y+ Z's hour's work =1/3   X + Y + Z's 1 hour's work =1/4	+1/3	=7/12   Y's 1 hour's work =	(7/12-1/2	)=	1/12	.   Y alone will take 12 hours to do the work.   12hours
<result>C</result>
X can do a piece of work in 4 hours; Y and Z together can do it in 3 hours, while X and Z together can do it in 2 hours. How long will Y alone take to do it?