Verb conjugation of "vendere" in Italian

What do we do about the numbers? I skipped them because I wasn't sure. Because it is possible that somebody wants to know how to say 15 in Spanish. He should write out the word as 'fifteen', not as digits.
The last sentence is the hardest in the entire series. Writing may bore some people, but it is considered the best training in language learning. It is a skill that can lift you from intermediate to advanced level. Do not neglect it.
Do not worry, please, all is well here. I find it fascinating how fast you can write texts in foreign languages. I know how hard it is, and I congratulate you. Waiting to your next email.