Answer:
78 buttons left
Explanation:
I multiplied 24 children by 3 buttons because each child took 3 buttons and I got 72 buttons taken.
Then I subtracted 150 buttons which is the starting number by 72 buttons (the amount taken by the child's) to get 78 buttons left in the box. ( I just separated negative 72 buttons into -50 and -22 to make it easier)