In a CROSS JOIN (also known as a Cartesian join), each row from the first table (emp) is joined to every row of the second table (dept). When we apply the filter for job = 'MANAGER' and dept.deptno IN (10, 20), we are restricting the results to managers in departments 10 and 20.

From the given data:

There are 2 managers in department 10 (CLARK and KING).

There is 1 manager in department 20 (JONES).

With a cross join, each of these emp records will join with each dept record where deptno is 10 or 20. Since there are two departments (10 and 20) in the dept table, each employee will match with two departments.

Therefore, the result set will be:

CLARK with accounting (dept 10) and research (dept 20)

KING with accounting (dept 10) and research (dept 20)

JONES with accounting (dept 10) and research (dept 20)

That gives us a total of 6 rows, which means the correct answer is B: 6.