4a)
According to Ohm's law (Current) = (Voltage)/(Resistance)
Given the values: (Current) = 9V / 470 Ohm = 19.1 mA
The current through the LED is 19.1mA, or 0.019A
4b)
(max current) = (voltage)/(min resistance) =>
(min resistance) = (voltage)/(max current) = 6V / 0.05 A = 120 Ohm
The resistor must be at least 120 Ohm, otherwise the LED will fry.
