The inverse of the inverse of a function gives the function
i.e f−1(f−1(x))=f(x)f^{-1}(f^{-1}(x)) = f(x)f−1(f−1(x))=f(x)
f−1(x)=x+14f^{-1}(x) = \frac{x+1}{4}f−1(x)=4x+1
Take y = x, so
f−1(y)=y+14f^{-1}(y) = \frac{y+1}{4}f−1(y)=4y+1
Let x=f−1(y)x = f^{-1}(y)x=f−1(y),
x=y+14 ⟹ 4x=y+1x = \frac{y+1}{4} \implies 4x = y + 1x=4y+1⟹4x=y+1
y=f(x)=4x−1y = f(x) = 4x - 1y=f(x)=4x−1
