How do I calculate the heading to steer in this example? At 1415 an aircraft was overhead a VOR maintaining radial 215°, en
  route for B, heading 210°(M). At 1430, the pilot decides to return to
  the VOR. The heading to steer is...


The answer is given as 040°(M), I'd just like to know the steps to calculate the answer.
You are holding 215 by compensating for a crosswind using 5 degrees of heading change.

The opposite of 215 is 035.

You must compensate by holding 5 degrees of heading change past 035.



Presumably, the fact that you're 30 minutes flight time away from the VOR when you turn gives the pilot sufficient time to reestablish themelves on course. Thanks @MichaelHall!