Answer:
Metaphor
Step-by-step explanation:
A metaphor is a figure of speech applied to a person or object (can even be an action sometimes) to which the phrase used is not literally applicable.
For example: Jasper the cat was the apple of my eye. Is he an apple? Of course not, Jasper is a cat. This means he was the best in that person's eye.
Similar to this case, winning the essay was this person's best part of their perfect day.
Hope this helps! :)