Answer:
f^-1(x) = 1/(5x - 3) (See explanation for alternate answer)
Explanation:
Assuming you meant f(x) = 1/(5x) + 3/5
y = 1/(5x) + 3/5
(I like to substitute x and y early on)
x = 1/(5y) + 3/5
5x = 1/y + 3
1/y = 5x - 3
f^-1(x) = 1/(5x - 3)
Assuming you meant f(x) = 1x/5 + 3/5
y = 1x/5 + 3/5
x = 1y/5 + 3/5
5x = y + 3
f^-1(x) = 5x - 3