A can lay railway track between two given stations in 16 days and B can do the same job in 12 days. With help of C, they did the job in 4 days only. Then, C alone can do the job in
a) 9 ? days
b) 9 ? days
c) 9 ? days
d) 10 days
a) 9 ? days
b) 9 ? days
c) 9 ? days
d) 10 days