Wolfram Alpha Wrong Again?

This was an amazing problem asked by someone else named Andre Amare Bernardo:

Here's how I attacked it:

I had tons of fun solving it, can't you tell?

Yet when I checked my answer with WolframAlpha, I received this:

It could be possible that I made a mistake somewhere, yet I don't get where the mistake could be. Could you make a video about this? Also, please credit Andre for the problem if you decide to do so!

Thanks for reading along! Bye!