Okay, so to get the inverse function, you need to isolate the x first.
You can do this by multiplying by 4. Then, -2 to get just 3x and finally divide by 3 so that you just have x on its own. If we write this all out, we get (4x-2)/3.
Next, we need to substitute 24 into x's place. So, we have ((4x24)-2)/3. Then, we can just simplify. 4x24=96. 96-2=94. 94/3=32.6.
Hope this helps :)