6. (3 points) There are 38 people playing table tennis on 15 tables simultaneously. The number of tables for singles is $\qquad$  
The number of tables for doubles is $\qquad$.
【Solution】Assuming all 15 tables are doubles, the number of people would be: $15 \times 4=60$ (people), which is 60
$$
-38=22 \text { (people), }
$$

It is known that each doubles table has $4-2=2$ (more people) than a singles table,
So the number of singles tables is: $22 \div 2=11$ (tables),
Thus, the number of doubles tables is: 15 - 11=4 (tables);
Answer: There are 11 singles tables; 4 doubles tables.
Therefore, the answer is: $11 ; 4$.