I hope this is the right place to ask this question.

In a library called Xsteam there is a function s_pT which gives a value, s, from two inputs p and T. I am in a situation where I have a value s and a input value for T but am seeking p. So if the function can be written like this:

s = Xsteam('s_pT',p,T)

And in my case I know that s = 6.5 for an unknown p and T = 600. Which methods can I use to get out p from this situation? Surely that value must be avialiable?