Answer:

This is how you do it in Multiples of 9 add it to the last number Ex. 54+9=63 63+9=72 72+9=81 and so on.

In 18 it would ba the same adding 18 the last number of multiples 54+18=72 72+18 and so on.

Same with 27. 54+27 and so on

Also in 54 the last multiple number add it to 54 and so on