Is a business letter, what is the purpose of the heading?

The heading of a business letter should contain the return address (usually two or three lines) followed by a line with the date. The heading is indented to the middle of the page in the modified block and semi-block styles. It begins at the left margin in the block style.

The heading indicates where the letter originates and when it was written, it also contains the return address. Sometimes it is necessary to provide other means of communication such as a phone number, email etc. so they can get back to you faster, easier, and cheaper.
The heading is used as a way for them to contact you with any information etc. It is also important if the business letter is going to be put in a file(which many are) so that they can see when it was written and by who, so they know if it is still relevant to them. 

Select the word from the list that best fits the definitionstates the the universe is expanding

According to my researches, the statement   "the factual information allows you to judge how credible the analysis in the source is." is not true. a factual information does not judge any credible analysis because it shows facts that are generally known by everyone.