Since $X$ is a primary key, on deleting $(3, 4)$, all the foreign key occurrences of $3$ will also be deleted: $(4, 3)$.
We've deleted $4$, which was also primary key in $(4, 3)$, its foreign key occurrences will also be deleted: $(2, 4), (6, 4)$.
$2$ and $6$ are also deleted, so their foreign key occurrences will also be deleted: $(5, 2), (7, 2)$.
Likewise, $5$ and $7$'s key foreign key occurrences will also be deleted: $(9, 5)$.
And that deletes whole of the tuples of the table.