A can do a piece of work in 4 hours. B and C together can do it in 3 hours, while A and C together can do it in 2 hours. How long will B alone take to do it? Choices
A) 10 hr  B) 12 hr  C) 15 hr  D) 13 hr  E) 9 hr
A's 1 hour work = 1/4   12 hr+C 1 hour work = 1/3   A+C 1 hour work +  1= 
<gadget id="calculator">+  1</gadget>
<output>1</output>
1/3   A+C 1 hour work = 1/2   A+12 hr+C 1 hour work  +  1= 
<gadget id="calculator"> +  1</gadget>
<output>1</output>
1/2   A+12 hr+C 1 hour work = 1/4 + 1/3 +  1= 
<gadget id="calculator">+  1</gadget>
<output>1</output>
1/4 + 1/3= 7/12   12 hr's 1 hour work = 7/12 - 1/2 = 1/12   12 hr alone will take 12 hours to do the work   Answer is 12 hr
<result>B</result>
A can do a piece of work in 4 hours. B and C together can do it in 3 hours, while A and C together can do it in 2 hours. How long will B alone take to do it?