to find the inverse "relation" of any equation, simply do a switcharoo on the variables, now, if the resulting inverse "relation" happens to be a function, as the "vertical line test" has it, then is also an "inverse function" and as 3a said it, yes, only one-to-one functions have inverse functions
so let's see Numliters(t) then

now, name wise, heck, you can call it whatever you want, even spaghetti

anyhow...that's the inverse function