Charles is failing to <u>recall</u> information from his long-term memory.
Explanation:
In every individual, the ability to recall an information differs across board with some individual being able to recall information faster than others that it took slowly. This is different from memory loss which is an inability to recall something due to head injury or old age.
In the case of Charles, it was just a temporary situation which might has been as a result of him being under pressure in the examination hall.
While taking his statistics exam, Charles is trying to remember a statistical formula that he studied the night before. However, he cannot seem to recall the correct information. Charles is failing to RETRIEVE information from his long-term memory.