To find the inverse of a function, simply switch the x and y, then set it equal to y:
[tex]x = \frac{1}{2} y + 4 \\ \\ x -4 = \frac{1}{2} y \\ \\ f^{-1} (x) = 2x-8[/tex]
Next, plug 4 in for x:
[tex]f^{-1} (4) = 2(4)-8 \\ \\ f^{-1} (4) = 8-8 \\ \\ f^{-1} (4) = 0[/tex]
