[4,2] is the right answer. If you delete 2,4 then the graph looks like:

4 1
| |
v v
2 < - 5 - > 3

which is not a rooted tree. Recall the definition for rooted tree, in the problem statement:

A rooted tree is a directed graph such that, there is exactly one node (the root) for which all other nodes are descendants of this node, plus every node has exactly one parent, except for the root node which has no parents.

Here, 1 or 4 are the only nodes with no parents; furthermore, 4 is not a descendant of 1 and vice versa.

If you delete [4,2], then the graph looks like:

4 1
^ |
| v
2 < - 5 - > 3

which is a rooted tree (1 is the root.)