Two large containers A and B of the same size are filled with different fluids. The fluids in containers A and B are maintained at 0 C and 100 C, respectively. A small metal bar, whose initial temperature is 100 C, is lowered into container A. After 1 minute the temperature of the bar is 90 C. After 2 minutes the bar is removed and instantly transferred to the other container. After 1 minute in container B the temperature of the bar rises 10 C. How long, measured from the start of the entire process, will it take the bar to reach 99.9 C?