There is no particular number, you have to find it through an equation: I.M.A. = Radius (wheel) / Radius (axle)
Stem cells: Undifferntiated cells with the ability to differentiate (another word for develop/change) into other cells with specialized purposes such as nerve cells.
Someone with neurological damage could benefit as they have received nerve damage; if stem cells could differentiate into nerve cells that could be transplanted into that someone without their body rejecting it, the neurological damage could be reduced.
One ethical implication is that stem cells could be harvested from zygotes.
