Mystic Syn

So, I've been doing math for the past few hours or so, and this specific question was giving me a hard time, but I wasn't going to give up that easily. There's an option on my math course if I were to get the question wrong, I could do a similar question that was not the same one.

Anyways, I put in a random number for this question that had me stuck, and it turned out to be the answer and I sat there like: •-•