Tony and Harry had some stamps. After Tony gave c stamps to Harry, he had 8 more stamps than Harry. How many more stamps than Harry did Tony have at first?
Let's say we each have two apples.
If I give you one apple, you have three and I have one. So the difference is 2 apples.
If I give you two apples, you have four and I have none, the difference is 4.
We conclude therefore that for every apple I give you, the difference increases by twice what I gave you.
Can you solve the problem now?