Please help!! second time posting !! algebra question, about functions! 
 how do you inverse/isolate y in this question, “f(x) = x-3/x” or y = x-3/x
 I know it becomes y=x-3/x, then becomes x = y-3/y,
 (By the way, the bottom denominator y is over y-3),
 I know the answer is f^-1(x) = 3/1-x, I just don’t understand how you isolate y in this specific question, thank you so much!!