0.067 is anything but constant. You can't calculate it, you have to measure the 3 variables first.
sort of empirical determined variables, most important to determine is how the original variables influence "the constant", linear exponential quadratic chaotic etc.
If that is determined one can derive formulas and calculate it.
This is sometimes trivial, but often rather complex as the variables you start with and measure may not be the "root" variables but depend on an underlying mechanism.
Furthermore the "root" variables may change in time which causes the need to recalculate the "constant" constantly. Rules of thumb and approximations maight become the only workable solutions.