Which is better: voluntary fasting or studying during exam days if fasting negatively affects one's studying?

If observing a supererogatory fast affects your studies, it is better for you to break your fast and strengthen yourself to complete your studies, then fast afterwards. It is hoped that Allah will record the reward for you due to your intention, because what prevented you from fasting was hardship. The Messenger of Allah, peace and blessings be upon him, said: "If a servant falls ill or travels, what he used to do when he was a resident and healthy will be written for him."