Physics
posted by Work needed! .
The length of a spring increases by 7.2 cm from its relaxed length when a mass of 1.4 kg is hanging in equilibrium from the spring. (a) What is the spring constant? (b) How much elastic potential energy is stored in the spring? (c) A different mass is suspended and the spring length increases by 12.2 cm from its relaxed length to its new equilibrium position. What is the second mass?

Work is indeed needed. Why don't you show any?
The definition of spring constant (k) is force divided by deflection.
Elastic energy is (1/2)kX^2
Deflection is proportional to mass.
If you are not going to attempt problems like this, you are not going to learn physics. 
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