You can do this in one event.
Have an instance variable or boolean i.e. isUsed on the plate.
Have 2 variables on the burger which is its current position (for cancelling). curPosX and curPosY.
Then the event is Burger on drop, if overlapping plate and plate.isUsed is set to false, set burger position to plate and set plate.isUsed to true, Else set burger position to burger.curPosX, burger.curPosY (its position before it was picked up).