Question 72432
Let {{{3/x=z}}}. 
Then, {{{x = 3/z}}}.


Hence the expression {{{f(3/x)=2x-1}}} becomes {{{f(z)=2(3/z)-1}}} i.e. {{{f(z)=6/z-1}}}


To find f(x) replace 'z' with 'x'.
Then, {{{f(x)=6/x-1}}}