Solve for R

PV = nRT

When everything is multiplied by the letter you are solving
for and there are no additions to it, all you have to do is
divide both sides by the factors that are multiplied by that
letter.

So we divide both sides by nT so they can be canceled leaving
only the R



Now we cancel away the n and the T on the right



 = R

And if you prefer you can reverse the equation:

R = 

Edwin