A student performs the simple harmonic motion experiment. He varies the mass, m, added to a 175 g spring suspended vertically and measures period, T. After plotting T^2, he obtains a slope of .380 s^2/kg, and a horizontal intercept of -.065 kg.

a. find the spring constant
b. the fraction of the mass of the spring which effectively oscillates with the same amplitude as the added mass.

Please explain.