You can use Task in c# 4.0 for threading. Task take care of threading internally so it is safer than dealing with threads.
Example on how to work on your program using Task is:
Task<int> t1 = Task<int>.Factory.StartNew(() => m.SumTest(5));
Task t2 = Task.Factory.StartNew(() => m.Divide());
var sumResult = t1.Result;