I believe 3b/6a which could reduce to b/3a.
Answer:

Step-by-step explanation:
To find the inverse of a function, simply switch the 'x' and 'y' variables. Substitute in 'y' in the place of f(x) for this purpose:
y = 2x - 10
Switch positions:
x = 2y - 10
Add '10' to both sides to begin simplifying:
x + 10 = 2y
Divide both sides by 2:

This can be rewritten as:

Therefore, the inverse of the function is:

On which one? You did not provide anything for me to help you with.
Cubic functions usually look like an S
The sequence seems to be that you add 1 and then multiply by 2, and then add 1 and multiply by 3, so I would assume you do 9 + 1 = 10, and then multiply by 4 to get 40 as your next number. I hope this helps!