Which equation expresses the conservation of mechanical energy in a system where the only forms of mechanical energy are kinetic energy and elastic potential energy?

a.

1/2mvi2 + mghi = 1/2mvf2 + mghf

b.

1/2mvi2 + mghi + 1/2kxi2 = 1/2mvf2 + mghf + 1/2kxf2

c.

1/2mvi2 + 1/2kxi2 = 1/2mvf2 + 1/2kxf2

d.

mei = mef