This question tests Newton's First Law of Motion (the law of inertia), which states that a body continues in its state of rest or of uniform motion in a straight line unless acted upon by a net (unbalanced) external force. The crucial word is net: several forces can act at once, and what governs the motion is their vector sum, not any single force.

Here two forces act along the same horizontal line:

• An applied push of 30 N toward the right.
• A frictional force of 30 N toward the left (friction always opposes the tendency of relative motion).

Since they are equal in magnitude and opposite in direction, they cancel exactly. Taking rightward as positive, net force = (+30) + (−30) = 0 N. With zero net force, the acceleration is also zero because a = F_net/m = 0.

The box was initially at rest. Zero acceleration means its velocity cannot change, so a body at rest stays at rest. Therefore the box remains at rest — the forces are said to be balanced.

The box cannot accelerate to the right, since that would require a leftover rightward force, but friction has neutralised the push. It cannot slow down and stop, because it was never moving in the first place. And it cannot move in the opposite direction, because the net force is exactly zero, not directed leftward. (In reality static friction only rises up to a maximum; the problem simply tells us it matches the push at 30 N, keeping the object stationary.)