<image>In a rectangular water tank with a length of 60 cm, a width of 50 cm, and a height of 100 cm, water is injected into the tank using two inlet pipes, A and B. First, pipe A is opened, and after n minutes, both pipes are opened simultaneously. Based on the line chart, answer the following questions.
a. After how many minutes of only opening pipe A, do pipes A and B open simultaneously?
b. Pipe A can inject ____ cubic centimeters of water into the container per minute.
c. After both pipes A and B are opened, it takes ____ minutes to fill the tank.