Given f(x) = the quantity of 4x plus 1, divided by 3
solve for f-1(3).

First we need to find inverse function of f(x) which is written in a form of (f(x))^(-1)
That means that we are actually looking for function f(y) and we need to solve this equation for "y"

y=(4x + 1)/3
3y = 4x + 1
4x = 3y - 1
x = (3y - 1) / 4
f(y) = (3y - 1)/4

Now we simply put the value of 3 instead of y and find the
f(y=3) = (3*3-1)/4 = 2

Answer is 2