thankful or grateful

[Petrikova]

hello,
I would like to ask if there is any difference between the two adjectives and if in business correspondence we should use rather ferateful instead of thankful.
I would also like to ask about the ver to arrive, the rules says we arrive in town, city or country and arrive at if it is a building. Is it possible to say "arrive in the hospital" and if yes, why so,
thank you very much,
L.Petrikova

[Tdol]

In a letter, i would say that I would be grateful if...
I'd use 'thankful' to describe someone who expressed their gratitude, and not to describe my own.
I'd say I arrived at hospital.