We know that,

Probability of occurrence of an event

As 3, 6 are multiples up to 6, so the desired outcomes are 3, 6, and total outcomes are 1, 2, 3, 4, 5, 6

Therefore, total no.of outcomes are 6, and total no.of desired outcomes are 2

Probability of getting multiple of 3

Conclusion: Probability of getting multiple of 3 when die is thrown is