@windhamrules
Alas, the op originally specified 3 LEDs (at 3.5v) in SERIES.
So, R = E/I = (14.5 - 3*3.5)/0.020 = (14.5 - 10.5)/0.020 = 4/0.020 = 200-Ohms.
Sorry, 40-mA is just a bit much for the taste of many LEDs. And
you'll probably get just as much brightness and LIFE out of the LEDs if
they're driven at 10-mA, thus use a 400-ohm resistor in series with the
LEDs.