Please help with the following QM question regarding the Stern-Gerlach experiment.

(a) Our explanation of the Stern-Gerlach experiment was somewhat unsatisfactory, as it involved the use of classical forces constructed from the quantum mechanical z-dependent energy differences. Starting with p2 H = (1) 2m - 1B . S, with B ~ (Bo + az) z for some small a > 0, use the Ehrenfest theorem to show that 22 m at2 ( 2 ) = ya ( 5 2 ) . (2) Discuss why the (fully quantum mechanical) equation above leads to the result that Stern and Gerlach observed