Okay so here we go,
Multiples of 2 on a 6 sided cube are:
2, 4 and 6 which in probability terms is 3/6 (simplifies to 1/2)
Numbers greater than 3 are: 4, 5 and 6 which in probability terms is 3/6 (simplifies to 1/2)
The question says 'or' which means addition of probabilities.
1/2 + 1/2 = 1
Your answer is 1