The faces of the cube are numbered 1-6which set represent the favorable outcome of the event of getting a number less than 4,after rolled once

The favorable outcomes are getting a 1, 2, or 3. So the set representing the favorable outcomes is {1, 2, 3}.

The set representing the favorable outcome of getting a number less than 4 after rolling a cube once is {1, 2, 3}. This set contains the numbers that are less than 4 on the faces of the cube.