The answer to your question is the Origin
To calculate for the force in a spring, we use Hooke's Law which relates force and the displacement of the spring. It is said that the force is directly proportional to the displacement. So, it will have the equation F = kx where k is a constant and it is the spring constant.
F = kx
F = 45 N/m (0.03)
F = 1.35 N
Answer
given,
length of slender rod =80 cm = 0.8 m
mass of rod = 0.39 Kg
mass of small sphere = 0.0200 kg
mass of another sphere weld = 0.0500 Kg
calculating the moment of inertia of the system



using conservation of energy




we know,
v = r ω


v = 1.084 m/s
28 degrees celsius converts to 82.4 degrees in Fahrenheit :)
B, since it is the only one that actually conserves matter for certain. In each of the others, matter could still be imbalanced, since for A, for example, it could be 5 Carbons on the right and 5 Chlorines on the left, and that would not balance.