Answer:
The magnitude of force is 15.48 N.
Step-by-step explanation:
Given that,
Mass of the box, m = 12 kg
It is observed that it takes the box 6.8 seconds to travel 30 meters. We need ti find the magnitude of force. For this we must know the acceleration of the box. It is given by :

Here, u = 0

The magnitude of force is given by :

So, the magnitude of force is 15.48 N. Hence, this is the required solution.