Well, here is what i do not explain clearly in the book. As mein Freund Cheerio said, transistors are current devices. There is no direct link between voltage and transistor operation. I have to clearly explain this in the book. Transistors only amplify CURRENT. The voltage amplification is a sort of "byproduct" as a result of ohm's law: by increasing the current through a resistor (for example the collector resistor) the voltage drop across this resistor is increased.

That being said,we need to find a way to "convert" voltage into current. The easiest way is by using a resistor. Since the supply voltage for the base is constant, we can alter the base current with a series resistor (I=V/R). We need to drop it as low as required. How much? this depends on the collector current requirements and the hfe. Say we want 20mA collector current and the hfe is 100.. the base current must be 20/100=0.2mA or 200uA. So we use the ohms law to calculate what resistor we have to use on the base to allow only 200uA of current thorugh the base:

R=V/I = 5/0.2 = 25KOhm

As for the 16.6 to 35mA, as Cheerio already said, we always overpower the outputs. Since the transistor that i use can provide up to 800mA, there is absolutely no problem to double the current. This is how the 35mA comes out of the 16.6, not a typo