Mosfet

[mathrocks]

I'm having problems figuring out how to determine Kn which is the transconductance parameter of an NMOS MOSFET. For one of my problems I'm just given a graph of Id(drain current) vs Vd(drain voltage) and there are several Vgs(voltage b/w gate and source) curves on it and I'm asked to find Kn, Vtn(threshold voltage), and then the ratio of W/L (width/length).

I know to find Vth, but I have no idea how to figure out W/L and Kn from just a graph. I guess first of all what exactly is Kn....