All Zero Puzzle

Can you find correct numbers in some numbers?
This is a puzzle game that delete all numbers of question.
The rule is simple, but a difficulty increases step by step.

■Rule
(1) There are "Question panels" on top of the screen. There are "Answer panels" on bottom of the screen.
(2) You select an "Answer panel" and drop on a "Question Panel". Then number of "Question panel" changes.
(before: Q=3, A=2 ---> 3-2=1 --> after: Q=1)
(3) If all numbers of "Question panels" are zero (not minus), you clear the level.

■Feature
・All 200 level are free.
・The difficulty increases step by step.
・There is "Today's question". You can play a different game everyday. It is updated at 0:00(UTC+9).
・There is a support function. That is red panel which tells you possible of the correct panel.
・There is a support function. That is "undo" function.
・This game is a practice of "Addition" and "Subtraction".
・You can use a "Hint" function.
・There is a leaderboard (Game Center).
・There is not a time limit. You can think long time.