Helen said to Mary, "If you give me $$4$$ apples, I will have exactly as many apples as you." How many more apples does Mary have than Helen? 
Overseas Competition->Knowledge Point->Word Problem Modules->Questions Involving Sum, Difference and Multiples->Problems of Difference and Multiple->Differences and Multiples of Two Variables->Differences and Integer Multiples
Difference: $4+4=8$ 