How many hours will it take for all the students and teachers together to put up a tent?
A. There are 4 teachers and 7 students.
B. All the teachers working together can put up the tent in 5 hours while all the students working together can do so in 3 hours.

Statement A alone is insufficient, as there is no time given and statement B alone is sufficient, as the number of teachers and students are missing.

All the teachers can complete 1/5 of work in 1 hour and all students can complete 1/3 of work in 1 hour. Therefore in 1 hr they can complete 8/15 of work in 1 hour and total work will be completed in 15/8 hours.

$$\therefore$$ Statement B alone is sufficient.

=> Ans - (B)