An object with a mass of 3 kg is hanging from a spring with a constant of 8 kgs^-2. If the spring is stretched by 3 m, what is the net force on the object?

The net force acting the difference between the weight force, $F = m g$, acting downward and the spring force, $F = k x$, acting upward. The net force is $F = m g - k x$ (if we define downward as positive). $F = 3 \times 9.8 - 8 \times 3 = 5.4$ $N$ downward.