Hi there! It's late at night, but I am new to the forum and thought I could help you out a little bit!
It is mostly properly written. There are a few errors.
1. Dear MJ (if MJ is someone's initials, it should be punctuated as M.J.) Otherwise, you have a comma and a period after "Dear MJ." All you need is a comma unless this is a formal letter to a superior or a stranger, such as a boss or a person who interviewed you for a job. If it is a formal letter, it's best to follow your greeting with a colon and not a comma.
2. Regarding, "How is your business trip going on?" You don't need to say "going on" because "going" is already in present continuous form. Since the person's business trip is in process, it's simply said as, "How is your business trip going?" Similarly, this rule applies to the following sentences, as long as both the school year and the project are still continuing at the time the sentence is written. "How is your school year going?" or "How is your project going?"
3. When you write, "To improve their sales skills..." you need to be more clear to whom you're referring by using the pronoun "their." I imagine "their" refers to sales representatives, but because you haven't mentioned sales representatives before, using a pronoun without an antecedent is very confusing for the reader.
4. "Sincerely," is considered to be an appropriate closing at the end of a letter. It's no longer necessary to say "Sincerely yours," or "Yours sincerely."
5. Your closing, thus, should look like this:
(I am not sure why you placed a comma in between Carrie and Lee?)
I hope this helps!