Relation between motor RPM, gear ratio, and clutch when accelerating

Hello !

I'm making a vehicle controller script. And I want it to be the most realistic as possible, I've already made the steering, and other parameters, but I'm now making the script when accelerating. I'm searching a formula to calculate the motor RPM depending on the gear ratio and the clutch (engaged or not). I've searched, but as always it's calculating motor RPM from Wheel RPM, that's not what I want, I want to calculate motor RPM first, and then RPMs will go to the wheels (depending on clutch and gear ratio).

Does anyone know maths formula for that ?

Best regards,