Calculating the resistance of a 30m wire can be done, of course, and getting the voltage divider maths done should be rather easy.
However, that would result in a high pullup / pulldown resistor, the higher the better.
On the other side, high pullups are also called "weak" pullup resistors, and usually you are better off running a higher current, aren't you ?
Isn't the more interesting part some non-static influences? Isn't that about the capacity of the wire, rather than the resistance?
How do you calculate maximum frequency of your signal over a long wire?
If you deal with very seldom changing signals, wouldn't it be better to also add an extra capacitor, to short down electric noise?
How are the maths done when it's about considering wire length and signals?
I know Ohm's law, now I want to learn something beyond ...