Square wave Oscillator using 556 timer

How to calculate upper and lower trip point voltage if VCC is equal to 5v as shows in the diagram.
this is 556 timer
If any1 knws what formula can be used to find the trip voltages
thanks for your time.

The datasheet for the 555 and 556 shows that the upper trip voltage is 2/3rds of the power supply voltage and the lower trip voltage is 1/3rd of the power supply voltage due to the three series 5k resistors connected as reference voltages to the comparators and to pin5.

Why didn't you look at the datasheet?