The combined gas law contains 3 gas parameters: p, V, and T, but this does not mean that you have to use all of them in the calculations. After all, from Washington to New York you don't necessarily have to go through Tokyo. If any of the gas parameters are identical on both sides of the equation, it can be eliminated by reducing the combined gas law to the previous one (Amontons, Gay-Lussac, or Charles). These are historical laws that you should know about, but all tasks of this type should be calculated using the ideal gas equation that allows you to take into account different amounts of different gases (masses, moles). And at all, for these calculations, it is not necessary to know the value of the gas constant R in any units (we compare two different states of the same or different gases by dividing by sides both equations written for these states).