can someone help with this gmatclub q please

the explanations mentioned alligation (0 clue what that is and I'd appreciate any info on it below).

I got somewhere with ratios but got lost at some point in my math. unsure where, would really love a walkthrough on this!

https://preview.redd.it/y1245qy99fge1.png?width=958&format=png&auto=webp&s=8c742307de06ba9c73feb0cfdc9565cb816d9a95