@Nisverah
I think he meant "If your attack force clears 19 dungeons with no casualties and no injury[...]".
Also, 10 people get in the dungeon, 8 get immediately paid and leave, 2 clearing the actual dungeon... that's how I see this thing working.
Remember that in the previous dungeon, 8 people just left it without consequences (to bring pickaxes and smoke).
It's really badly explained, or translated (but I think explained is more likely). But I think what he actually meant is "With an attack force of only two people, you clear 19 dungeons. Now THAT would impress your father".