First, we should understand the spring constant. Different springs may have different spring constants. A spring constant tells us that how much force is needed to bring a 1-centimeter stretch in a particular spring. Here the force applied is 16 N and the change in length is 8 cm.(18-10). Now we divide 16 by 8 and we get 2. So 2 N force is required here to bring a 1 cm stretch in this specific spring. So, the answer is A. 2.0 N/cm.
