The full version of the formula can be expressed as
R = k(10g + s)
Where R, g & s are as above. k is an observing constant based on personal experience and instrumentation.
Back in the 1990’s when I used to observe the Sun I found my k was 0.8.
Deciding what was one or two active areas is very much a matter of experience (feeling), but a Stonyhurst Disc could be used as a somewhat crude guide (if you observe by whole disc drawing).