How do you calculate multiples of 3?

Answer 1

134 x 3= 402....

If you divide the number by 3 and if you have no remainder it is a multiple of 3...

Answer 2

If the sum of their digits is a multiple of three, the whole number is a multiple of three.

Answer 3

You start with 0 and add 3.Then add 3.

Then add 3.

Keep going until you get fed up, because the set of multiples will never end.