There is no better time to use the Law of Total Tricks than when partner preempts. As long as you don't have game interest, just "Follow the LAW" and bid to the 2-level with 8 trumps, the 3-level with 9, and the 4-level with 10.
In this quiz, assume matchpoints--but be aware of the usual "adjustment factors" such as flat shape, honors in the opponents' suit, vulnerability.