That's a pseudo formula. It multiplies two unknowns.
Show me mathematician who can solve such an equation.


Besides, his methodology in the book was popular, but also flawed. He compared two very different forces instead of comparing multiple different formations of different performance from the same force. He's voluntarily looking at datasets that are much farther away from ceteris paribus than necessary, which clouds the whole approach - and he used practically no advanced empirical tools as (which would be required for such a multi-input dataset).
It's a pseudo study that purports to deliver scientific results when in fact it's really only about his opinion.