Also, it's obvious that English isn't your first language--so let me give you a few helpful hints--just for your future studies.
(1) The spelling is "cancellation", not "cancelation". Use the website "dictionary.com" if you are in doubt about spelling.
(2) Whenever you are refering to something such as a car, a hand, a step--then the usage of "a" is appropriate. However, when refering to something that starts with a vowel--like "appealing letter", "erroneous statement", or "elephant", then you don't use "a", but use "an" instead. So this means it is "an appealing letter", "an erroneous statement", or "an elephant".
P.S. Good luck getting into UCSD and with your studies in the US or wherever you end up going to college.