Depends. 41-50 its in Yellow map which is Mushroom Rocks north. It has 40million Lp and takes alot of man power. By the way They hardly do the yellow maps.
51-60 is in the red map which is Mushroom Rocks South. It has 70million Lp and They do it every week and kill them all.
Kill 30 majins. When the boss is killed the NPC spawns and you turn in the quest. You can take the quest as many times as you want. The Boss spawns when its 100%