Answer:
i believe the best answer would be C, useful!
Explanation:
well, looking over the other answers available:
a. difficult doesn't make sense, as it wasn't a difficult system to implement, and he did it rather easily due to how simple it was.
b. thoughtless doesn't make sense, because he implemented this system to reduce prices and make it so that more people could send letters.
d. careless doesn't make sense, as this system was implemented after a lot of trial and error and careful consideration.
so, c would be the most accurate! especially because we still use this system today. hope this helps! ☆
