How can you use a formula to find simple interest ?

One of the inventors of integrated circuits observed that the number of transistors that fit on an integrated circuit will double every 24 months. what type of relationship most appropriately models this situation?

If f(x) =3x-2 and g(x) =2x+1 fins (f+ g) (x)

If f(x)=3x+1 and f^-1=x-1/3, then f^-1(7)=