Determining potentiometer sensor output resistance with parallel resistor
Don't let the fact that there is a potentiometer in the circuit confuse you.  In any one setting, you can replace the potentiometer with two fixed resistors.  Once you have done that, you have a simple 4-resistor network to solve.

Solve this at as many pot settings as you like to get a graph of voltage as a function of pot position.

With a little extra math defining the two resistors you are modeling the pot as, you can write down the closed form equation of output voltage as a function of pot position.