Answer:
a. A 25-N force acts of the left side of the marble at the same time as a 25-N force acts on the right side of the marble.
Step-by-step explanation:
When trying to balance an object, you must keep the same amount of weight on each side to keep it in the middle. Think of a seesaw: whatever side has more weight pressure is the side that falls first. Hence, the correct answer is A.