Calculating pair price to USDT

Hi

I would like to know how to calculate the pair address in two ways, e.g. BNB/Safemoon

Given: reserveA(BNB) and reserveB(Safemoon)

The price for 1 Safemoon is calculated reserveA / reserveB

But I don't know how to calculate the price for USDT? Can someone help or know it?