I agree with the math of both of the previous answers, just a question regarding wording: the question asks for "How many days do they need to finish the same job?," which in my mind is the 3 days that the 6 workers use, PLUS the 3 days that the 10 workers use, making the answer D. Thoughts?
I originally picked D as well, for the same reason.. but after reviewing it again.
"how many days do they need to finish
the same project?"
well the project as a whole takes 6 days, but only 3 days left to finish it.