I assume you mean the inverse function. To find the inverse function of a given function, start from the expression [tex] y = f(x) [/tex] and solve for x:
[tex] y = \dfrac{3}{4} x [/tex]
Multiply both sides by 4:
[tex] 4y = 3x [/tex]
Divide both sides by 3:
[tex] \dfrac{4}{3}y = x [/tex]
So this is the inverse function.