#### Answer

(a) The two forces must be acting in the same direction.
(b) The two forces must be acting in perpendicular directions.
(c) The smallest magnitude of the net force occurs when the two forces are acting in opposite directions. In this case, the magnitude of the net force is 1.0 N

#### Work Step by Step

(a) If the net force has a magnitude of 7.0 N, then the two forces must be acting in the same direction. In this case, the net force is 3.0 N + 4.0 N which is 7.0 N
(b) If the net force has a magnitude of 5.0 N, then the two forces must be acting in perpendicular directions. In this case, the net force is $\sqrt{(3.0 N)^2 + (4.0 N)^2}$ which is 5.0 N
(c) The smallest magnitude of the net force occurs when the two forces are acting in opposite directions. In this case, the magnitude of the net force is 4.0 N - 3.0 N which is 1.0 N.