6、Taking the train from City A to City B, it initially took 19.5 hours at the beginning of 1998. In 1998, the train's speed was increased by $30\%$ for the first time, in 1999 it was increased by $25\%$ for the second time, and in 2000 it was increased by $20\%$ for the third time. After these three speed increases, the train journey from City A to City B only takes $\qquad$ hours.
6. Solution: According to the problem, when the distance is constant, speed and time are inversely proportional. $19.5 \div(1+30 \%) \div(1+25 \%) \div(1+20 \%)=19.5 \times \frac{100}{130} \times \frac{100}{125} \times \frac{100}{120}=10$ (hours) Answer: It takes only 10 hours to travel from City A to City B by train.