Two boxes (b1 = 23 kg and b2 = 57 kg) are being pushed across a horizontal frictionless surface, as the drawing shows. The 48-N pushing force is horizontal and is applied to the 23-kg box, which in turn pushes against the 57-kg box. Find the magnitude of the force that the 23-kg box applies to the 57-kg box.

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To find the magnitude of the force that the 23-kg box applies to the 57-kg box, we can use Newton's third law of motion, which states that for every action, there is an equal and opposite reaction.

Let's break down the problem step by step:

1. Identify the action and reaction forces:
- Action force: The pushing force applied to the 23-kg box. Its magnitude is given as 48 N.
- Reaction force: The force that the 23-kg box applies to the 57-kg box.

2. Apply Newton's third law of motion:
According to Newton's third law, the reaction force exerted by the 23-kg box on the 57-kg box is equal in magnitude and opposite in direction to the action force applied to the 23-kg box. Therefore, the magnitude of the force that the 23-kg box applies to the 57-kg box is also 48 N.

So, the magnitude of the force that the 23-kg box applies to the 57-kg box is 48 N.