What is the PSI on tire ST 245-75R-17.5?

120lbs on a trailer,the standard is printed on the tire.dual or single

The tire pressue depends on what vehicle you have this tire mounted on. The PSI listed on the tire sidewall is the maximum pressure they tire can handle not the correct pressure for the vehicle it is mounted on. The correct pressure for your vehicle/trailer will be listed in the owners manual and on the drivers door post or on the trailer.