How to solve the (b) circuit?
From the question:


  Can I guess the voltage of 200 &Omega;? (Example, 6.2 - 0.7 = 5.5).


This is correct. From that you can work out the current through the 200 &Omega; resistor and when you have the &beta; value you can work out the LED current.

From the comments:


  ... then I need to add 0.7 instead - 0.7 ...


When you are making statements like this you need to make it clear where the reference is. If we are measuring from GND then, yes, you add the voltage of the base-emitter drop.