Operational amplifier - comparator with LED
Assuming that the input differential voltage is not restricted internally with protection diodes, the voltage at the inverting input is the potential divider formed by RT and RH acting on the 15 volt supply. The non-inverting terminal has 7.5 volts because the two resistors are equal (R=R).

Not considered in this simple explanation are: -


Input offset voltage (maybe up to 10 mV)
Input bias currents (pA to uA) that make a small error in the analysis.