Pipe A alone can fill the tank in 4 hours, while pipe B alone can fill it in 6 hours. Pipe C can empty the whole tank in 4 hours. Mr Ram Bishan, whose job is to observe the filling of tank, opened the pipe A and B simultaneously to fill the empty tank. He wanted to adjust his alarm so that he could open the pipe C when the tank was half-filled, but he mistakenly adjusted his alarm at a time when his tank would be 3/4th filled. Now please find the time difference between both the cases, to fill the tank fully: