How Do You Calculate Acceleration with Friction Forces Involved?

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To calculate the acceleration of the box, first determine the net force by subtracting the friction force from the applied force. The applied force is 200N to the right (positive), and the friction force is 100N to the left (negative), resulting in a net force of 100N to the right. Using the formula F = m * a, where F is the net force and m is the mass, the equation becomes 100N = 20kg * a. Solving for acceleration gives a = 5 m/s² to the right. Understanding the direction of forces and applying basic subtraction is key to solving this problem.
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I am not getting forces at all. I 'm not sure of what to do. Here's the question:

A box is resting on a flat surface. The box has a mass of 20KG and a force of 200N is pushing the box to the right. The force of friction acting on the box is 100 N to the left. What is the acceleration of the box?

I know that the sum of the forces=Mass X Acceleration. But I am not sure what numbers to put in.
 
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Consider the forces that act along the line of motion (left-right forces that is , the box is not moving up or down is it?). Call forces to the right "positive. Call forces to the left "negative." What is the sum of all the left-right forces? (Hint: it involves a little mathematical trick called "subtraction.")
 
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