8. (10 points) Two small rulers form a set of rulers, and the small rulers can slide along the large ruler. Each unit on the large ruler is marked with a natural number. The first small ruler divides 11 units on the large ruler into 10, and the second small ruler divides 9 units on the large ruler into 10. The starting points of both small rulers are 0, and they are both marked from 1 to 10. Now, measure the distance between points A and B, where point A is at the 0 unit on the large ruler, and point B is between the 18th and 19th units on the large ruler. When the 0 unit of the first small ruler is placed at point B, its unit 3 coincides exactly with a unit on the large ruler. If the 0 unit of the second small ruler is placed at point B, then the \_\_\_\_\_ unit of the second small ruler coincides exactly with a unit on the large ruler.
【Analysis】According to the problem, the unit ratio of the first small ruler to the large ruler is 11:10. The unit 3 of the first small ruler is equivalent to 3.3 units of the large ruler (calculated based on the ratio). 3.3 of the large ruler and 18.7 can be added to get an integer, so the 0 of the small ruler corresponds to the unit 18.7 of the large ruler. For the second small ruler, starting from the 0 unit, the unit corresponding to an integer on the large ruler between 1 and 10 must be 18.7 plus a number ending in 3, meaning the decimal part of the added number is 3. According to the ratio of the large ruler to the second small ruler 9:10, when the second small ruler is 7, the unit of the large ruler has a decimal part of 3.

【Solution】Solve: $11: 10=?: 3$
$$
?=3.3
$$

The point $B$ located between units 18 and 19 should be: 18.7
18.7 can only be added to a number (let it be $X$) whose last digit is 3 to make a whole ten number.
? is a natural number between 1 and 10, so only $?=7$ meets the condition.