Looks like it's Pearson's Square or the Box Method: https://chemistry.stackexchange.com/questions/111440/is-there-a-name-for-this-algorithm-to-calculate-the-co

Looks like it's Pearson's Square or the Box Method: https://chemistry.stackexchange.com/questions/111440/is-there-a-name-for-this-algorithm-to-calculate-the-concentration-of-a-mixture-o https://chemistry.stackexchange.com/questions/111440/is-ther...