Figured it out!
An obvious first step would be to divide each side of the first equation by the corresponding side of the second equation.
Are little p and big P the same variable? In the final equation they don't appear so I would assume you solve for P in one equation and plug it into the other equation for P.
Sorry they're the same variable.
I don't know how this would go though? Divide both sides by P / bd2 to give bd2 = aR2T4 / p / bd2?
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