Answer:
Try listing reasons you were well behaved for a period of time, try to make it sound emotional and important to you, use passionate words like, "I tried really hard in math class" etc.
Logos means logic
Pathos means Emotion
and Ethos means Credibility (so trust)
Include all of those in your answer, and you'll be fine!
Example:
Mom and dad, I think I deserve a special gift for my birthday. I tried unbelievable hard in geometry class, which I usually do terribly in! I managed to learn, and remember, hundreds of words in Spanish class, but most of all - I love you guys! I would do anything to make you guys happy, and I know you would do the same for me!
Just check my grades! They are magnificent!
That's why I think I deserve to get an iPhone XR for my birthday.
That's just an example...