Tracy, The article "a" has two pronunciations, a weak form "a" and a strong form (ei). The strong form of the article "a" pronouced (ei) is not used often. When used, it is used emphatically-- 1) to show contrast It is a (ei) solution, but not the only solution. 2) when stressing the indefiniteness of something. Question.....I lost my wallet. Have you seen it? Answer....... I saw a (ei) wallet, but I don't know if it was yours. The strong form emphasizes the indefiniteness of the article "a". 3) to stress singularity-- I have a (ei) cat and a (ei) dog. I have one cat and one dog. 4) to name a word-- This animal is referred to as a (ei) platypus. There are no strict rules for the use of the strong article a (ei). It's use is a conscious decision. Some people consider it's use incorrect or an affectation.

You need to study weak and strong forms. In this sentence, both uses of "a" should be weak and therefore pronounced /ə/ (and not /ei/).

the letter a has 4 different pronunciation long a like car short a like cat schwa like about and among /ei/ like able and face

Do you takl about single letter "A"? It's an alphabet A from ABC. if you read it slowly it can be "ei". "ə" is sounds more like "U", but it's also Ok in some way, I think it just an custum.