Brajen can paint a wall red in 10 hours while Ballari can paint h the wall completely in 12 hours. If Brajen and Ballari work alternately for an hour each starting when the wall has just cement on it till when it is completely painted red, how many hours will it take to paint the entire wall red?
1
13
2
12
3
\(\)\(10\frac{1}{2}\)
4
\(10\frac {5}{6}\)