Ok, here is is as taught

Vh the voltage you divide
Vm the voltage at the midpoint
Rh the resistor from Vm to Vh
Rl Thge resistor from Vm to ground
Ri the input impedance to ground of the device connected to Vm
Rx an intermediate value

The value of the voltage at the midpoint will be:

     Rl * Ri
Rx = -------
     Rl + Ri

     Vh * Rx 
Vm = ---------
     (Rh + Rx)     

Have fun,

Erik