I want to devise a function $f(x)$ such that $f(4) = 160, f(16)=80, f(28)=40$ and $f(40)=20$, as well as all the other values in between $4-40$. As in, the numbers between $4-12$ have a proportional value between $160-80$. Numbers between $28-40$ have a proportional value between $40-20$ etc.
The values on the left go up linearly and the values on the right go down exponentially.
I hope this makes sense. But would appreciate any help. Thanks