(A) method A
to find the inverse of a function, we do the two following steps:
1. exchange x and y (or f^(-1))
2. Solve for y in terms of x.
For the given problem,
y=3x-4
step 1: exchange x and y: x=3y-4
step 2: solve for y: x=3y-4 => 3y=x+4 => y=(x+4)/3 => f^(-1)=(x+4)/3