f^-1 means finverse
find finverse then subsitute 3 for x
to solve
replace f(x) with y
solve for x
switch x with y
replace y with finverse or f^-1
f(x)=(x+5)/3
y=(x+5)/3
3y=x+5
3y-5=x
3x-5=y
finvers=3x-5
fiinverse(3)=3(3)-5
finverse(3)=9-5
finverse(3)=4
why is it not listed again