I always have problems with gears should hire some engineer to teach for few hours to design gears. Ok guys I would appreciate it if someone could show me how can I calculate the following gears. The Design is not conceptual as I need the gears to mesh correctly but the gear box is flexible. I need to design 3 Gears. A, B, C. and gearbox as well

Gear A Diameter (addendum circle) 62.5 mm (flexible) 48 teeth

Gear B Diameter (addendum Circle) 40 mm (flexible dimension) 30 teeth

Gear C Diameter (Unknown) 20 teeth

I need center to center distance to come close to these dimensions can shift by few or more mm no problem

Gear A to gear B around 50 mm (flexible)

Gear B to gear C 31 mm flexible at 107 degree angle. flexible.

So now I need these gears to correctly mesh based on the above information. I need to see the calculations meaning how this was calculated Im trying to understand how its done.