The seamstress completes work on 1 garment with every transition.

Therefore,

new number of garments = old number of garments- 1+ number of garments brought by messenger.

^This with the constraint that the number of garments must remain between zero and three.

So for example, =probability of having two garments, then no garments. How can this happen? It cannot. This probability is zero.

=probability of having two garments, then one garments. How can this happen? Only if the messenger brings no new garments - the seamstress will complete one of the two garments during the transition, leaving one remaining. This is probability 0.3

etc