I need help with physics please help

What is the magnitude of the resultant vector round your answer to the nearest tenth

Find v(t), given acceleration a(t)=7j and initial velocity v(0)=k

1. explain how you calculate the net force in any direction on the box. 2. suppose an upward force of 15n is added to the box. what will be the net vertical force on the box? 3. what force could be applied to the box to make the net force in the horizontal direction zero? explain. 4. suppose a force of 25n to the right is added to the box. what will be the net force to the right?