Tony had a million marbles and megan gave him a thousand hundred how many marbles does tony have now

1,100,000 marbles
One million = 1,000,000
One hundred thousand = 100,000
1,000,000 + 100,000 = 1,100,000

It is useful for historians to write narratives so that history can be passed on from their point of view.  think about a story being told in third person, then think about it again being told in first person, by someone who actually experienced the event.