I have this question and I am wondering if someone can tell me the
formula and how they derived the answer (steps) - it is probably
simple, but I am learning this as I go :

Electronic
1) A simple circuit consists of a current limiting resistor in series
with an LED across a supply voltage of 5VDC. The forward voltage drop
is 1.5VDC and the forward current is 10mA. The series resistor would
have a value of:
a. 1kΩ
b. 500Ω
c. 350Ω
d. 100Ω