Joan has trouble reading. sometimes the letters get mixed up so that it looks to joan like a completely different word. she has difficulty with written tests but performs quite well on oral tests. joan's learning disability is most likely:

Joan´s learning disability is most likely to be Dyslexia, a condition based on the brain. It hinder reading, spelling, and writing, the brain of people who have dyslexia find it difficult to recognize or process certain types of information, this may include matching the sound of a letter and its symbol (such as the letter b making the sound be), and then mix them to make a word. Some people with dyslexia have no problems pronouncing or "decoding" words, but they may struggle to understand what they read. It could become very difficult for people with dyslexia to read in an automatic or, apparently, effortless manner.

Answer agnosia;