The default says J1 open, RE = 0R. RL will be (5 - 3.1) / 0.075 = 25R
No, you can not connect a 75mA load to an Arduino GPIO pin. But a backlight is normally always on. Hence you connect to 5V pin on Arduino.
If you want to connect to a GPIO pin, you have to limit the current to 20mA. e.g. RE=70R, RL=25R, J1 open..
Actually the 75mA LED will probably have a Vf = 2.9V @ 20mA.
If the backlight is designed for 75mA it will not be bright enough with 20mA.
Do not worry about exact maths for 5V. The series resistors are not very critical.
With a 3.3V supply and a 3.1V LED, you must use the correct calculation.
David.