The figure below shows the same ideal spring in three different situations.
First, without a mass hanging, the spring is unstretched.
Next with the blue mass hanging, the spring stretches.
Finally, with the red mass hanging, the spring stretches twice as much as it did with the blue mass.
How much energy does the hanging red mass store in the spring-mass system, compared to the amount of energy the hanging blue mass stores in the spring-mass system?