Answer:
3/2
Explanation:
You might want to review "inverse function."
The easiest approach here is to let f(x) = y = 4 = 3x - 1/2 and then solve for x:
8 = 6x - 1, or
9 = 6x, or
x = 1.5 or x = 3/2.
If this is correct, then evaluating f(x) = 3x - 1/2 at x = 3/2 results in 4:
f(3/2) = 3(3/2) - 1/2, or 8/2, or 4. So we are correct here.