So with the caveat that it's not clear what "-ax 8" is... presumably there should be an operator between the x and the 8?

The key is to understand what f^-1(x) is, the inverse function of x. It's very simple - if f(x) = some expression involving x, then given a value for x, you can find f(x). f^-1(x) just works in reverse (being the inverse function). If you know the value for f(x), and plug it in to the f^-1(x) inverse function, it will spit out the original value of x.

So, you don't actually need to know what f^-1(x) is. You're told that f^-1(52) = 4. That means that for f(x)=52, you have x = 4.

So just substitute these into your original equation for f(x). I'm going to assume the missing operator is a +, but it will be easy for you to adjust this if it's something else:

Glad I could help, but you should post additional questions separately on the site (this space is for follow-ups specifically related to the original task).

I can certainly see new questions being posted, so I don't think it's a glitch with the site as a whole - perhaps it's something to do with having multiple accounts? I am pretty certain that is against the rules and spirit of a site like this where reputation and history are important (for example, I will simply not take on large amounts of work from users with zero history, hidden identities or a history of failing to pay after work was completed, it isn't worth the hassle!).