For this case we have the following equation:

Where,
w: The weight of a spring in pounds
E: the energy stored by the spring in joules.
Substituting values we have:

Making the corresponding calculation:
Answer:
the approximate weight of the spring in pounds is:
i got 5.14cm i don´t know how much you are supposed to round though
36/42= 0.857142857 x 6=5.142857143
1 and 2 are the factors its a compatable number