A and B can do a piece of work in 7 days. With the help of C they finish the work in 5 days. C alone can do that piece of work in?  Choices.
A) 11 days  B) 66 days  C) 30 days  D) 77 days  E) 88 days
30 days = 1/5 – 1/6 = 1/30 =&gt; 30 days   Answer: 30 days
<result>C</result>
A and B can do a piece of work in 7 days. With the help of C they finish the work in 5 days. C alone can do that piece of work in?