Hi everybody. I am trying to write a formal letter, and I need some help with one sentence. I have written this: "I guess there are not any other requirements, except paying fees at the start of my stay, but if you knew there is something else, would you please let me know?" I am no sure about the tense of the verb to know (know or knew) and about the symbol ?, is it necessary? And, do you think sentences sounds good, I try to be very formal. Thank you in advance!