Hello Hanieh,
The center will provide you a calculator within the computer (like the basic one you have on your laptop). In fact the calculator is included in the PMP exam.
You have only one break during the exam scheduled at the 89th question, for 10 minutes maximum (not included in your 4 hours) : so you have 4 hours and 10 mn.
If you would like to take more breaks like I did, time on the exam will continue, it won't stop.
Please note that if you decide to accept taking the 10 mn break included in your PMP exam, you won't be able to review your 89 responses after the break.
You should review them before the 89th question ( I did not take the time to review I accepted and took the break but it would be better to review your responses)
Hope I answered your questions