Answer:
B). Excitedly.
Step-by-step explanation:
Context clues are defined as the hints or clues provided by the author that allows the readers to determine the meaning of a particular unfamiliar word.
In the given statement, the hint 'how someone will have to work if he/she has to solve a number of mathematical problems within an hour' helps in understanding that the word 'feverishly' stands for 'excitedly or with excitement and determination.' This determination is clearly suggested by the details like 'barely ever looking up as his pencil flew up and down.' Therefore, option B is the correct answer.