The force applied to the cart in the above Question by spring scale FA is still 10. The cart now moves toward the right with an acceleration also…

The force applied to the cart in the above Question by spring scale FA is still 10.5 N. The cart now moves toward the right with an acceleration also toward the right of 1.75 m/s^2. What is the magnitude of friction force? (Note: The spring scale FA is being pulled toward the right)