We know that the Sunflowers and Orchids must be shipped before the Zinnias, so we can start here:
S O Z _ _ _ _ _
Which flowers can be shipped 4th, immediately after the Zinnias? It helps to start by thinking of the flowers that cannot be 4th.
Can L? No, because Z - L. Can M? No, because T - M
We have now eliminated S, O, Z, L, M from the 4th spot. This leaves us with 3 flowers: R V T I don't see any reason why these 3 cannot be 4th. This is why B is the correct answer.