The formula to use is,
R= Number of teeth in ring gear
S =Number of teeth in sun (middle) gear
P= Number of teeth in planet gears
Tr Turns of the ring gear
Ts Turns of the sun gear
Ty Turns of the planetary gear carrier (the Y shaped thing )
R Ring gear teeth
S Sun gear teeth
P Planet gear teeth
$$( R + S ) ×Ty = R × Tr + Ts × S$$
Generically, one can consider this to be a transfer case. It's common in a four-wheel drive vehicle, although in such application, power is applied to rear only or front and rear. The concept is consistent, as a transfer case would provide the option to disengage power from one output and apply to the other.
In the process of researching this question, I ...