Let's analyze the problem:
- Total people: $X$
- Mailed letters: 7 people
- Bought stamps: 9 people
- Mailed packages but didn't buy stamps and didn't mail letters: 10 people

We want to compare:
Quantity A: Number of people who both bought stamps and mailed letters
Quantity B: Number of people who mailed packages but didn't buy stamps and didn't mail letters (given directly as 10)

Since 10 people mailed packages but did not mail letters or buy stamps, they belong exclusively to that group.

For Quantity A (people who bought stamps and mailed letters), we know the total who mailed letters is 7 , and the total who bought stamps is 9.

The number of people who both bought stamps and mailed letters (the intersection) could be found if we had the total number of people $X$, or other overlaps like those who mailed packages but bought stamps or mailed letters.

Without additional information, the smallest possible intersection is:

$$
\(\max (0,7+9-X)\) .
$$


The largest possible intersection is:

$$
\(\min (7,9)=7\),
$$

since intersection can't exceed the smaller group.
So depending on $X$, the number of people who both bought stamps and mailed letters is at most 7.

Given Quantity $B=10$, the exclusive group mailing packages with no stamps or letters is 10 , which is more than the maximum possible intersection.

Therefore:
- Quantity A (intersection of stamps and letters) \( \leq 7\)
- Quantity B $=10$

Hence, Quantity B is greater.
Final comparison: Quantity B > Quantity A.