Chemists typically deal with $"litre"$ quantities of gases, and typically measure $"pressure"$ in units of $"atmospheres"$. Of course, both physicists and chemists tend to use $"degrees Kelvin"$ as units of absolute temperature (mind you, there is a $"Rankin"$ scale).
Given this, for chemists, $R$ is typically used as $0.0821*L*atm*K^-1*mol^-1$. There are other conventions, notably, $R=8.31*J*K^-1*mol^-1$, which requires volumes in $m^3$. All of the gas constants, and their units, should be supplied to you in an exam as supplementary material.
