A nine year old wrote this problem. Can you solve it? Viral Math Problem

This math problem went viral after being posted in 2020.
Celeste Ng tweeted 'At dinner, nine year old made up a math problem and made his father and me solve it. Our attempt at simultaneous equations got really complicated. We figured it out via guess and check, but I still think there has to be a more elegant way.'
Can you solve the nine year old math problem using both guess and check and the elegant way - using algebra?

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