In how many days will B alone complete the work? I. A and B together can complete the work in 8 days. II. B and C together can complete the work in 10 days. III. A and C together can complete the work in 12 days.

(A + B)'s 1 day's work = 1/8 ..........(i)
(B + C)'s 1 day's work = 1/10 ..........(ii)
(C + A)'s 1 day's work = 1/12 ............(iii)
Add the equation (i), (ii), (iii)
2(A + B + c)'s 1 day's work = 1/8 + 1/10 + 1/12
(A + B + C)'s 1 day's work = 1/2[1/8 + 1/10 + 1/12] ..........(iv)
Subtracting Eq. (iii) from Eq. (iv), we get B's 1 day's work.
then, required number of days = 1/(B's 1 day's work) .
So we need all above 3 statements to solve the given question.