On executing the given query, the tuple that got deleted from relation A is (1, 1).
The tuples in relation to B referring to the value a1 = 1, will also get deleted due to the On delete cascade. Therefore, the tuples (1,1), (2, 1), (3, 1) will get deleted.
Therefore, the remaining tuples in relation to B are 3, which are (4, 2), (5, 2), (6, 4).
On deleting values 1, 2, 3 of b1 form B, every tuple from C referring to these values will get deleted.
Therefore, the tuples that will get deleted from C will be (1,1), (2, 1), (3, 2), (4, 3).
Therefore, the number of tuples present in C are 2 which are (5, 4), (6, 6).
Therefore, the total number of tuples present in B and C after running this query are 2 + 3 = 5 tuples.