Aperson who learns best by hearing is known as a(n) learner

I believe the answer is: Auditory Learner

Auditory learner tend to be able to obtain more focus if the flow information that they have rely mostly on their auditory sense.
Due to this inherent talent, the most efficient way of learning for them would be the learning process by utilizing media such as audiobook or pre-recorded lectures.

3. i would say one, but one is not prime nor composite.