Two horizontal forces, F1 and F2, are acting on a box. F2 can point either to the right or to the left. The box moves only along the x axis. There is no friction between the box and the surface. Suppose that F1 = +2.4 N and the mass of the box is 4.8 kg. Find the magnitude and direction of when the acceleration of the box is
(a) +7.1 m/s2,
(b) -7.1 m/s2, and
(c) 0 m /s2.